Hour to Century Converter
Convert hours to centuries with our free online time converter.
Quick Answer
1 Hour = 0.00000114 centuries
Formula: Hour × conversion factor = Century
Use the calculator below for instant, accurate conversions.
Our Accuracy Guarantee
All conversion formulas on UnitsConverter.io have been verified against NIST (National Institute of Standards and Technology) guidelines and international SI standards. Our calculations are accurate to 10 decimal places for standard conversions and use arbitrary precision arithmetic for astronomical units.
Hour to Century Calculator
How to Use the Hour to Century Calculator:
- Enter the value you want to convert in the 'From' field (Hour).
- The converted value in Century will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Time category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Hour to Century: Step-by-Step Guide
Converting Hour to Century involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Hour = 1.1408e-6 centuriesExample Calculation:
Convert 60 hours: 60 × 1.1408e-6 = 6.8448e-5 centuries
Disclaimer: For Reference Only
These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.
Not for professional use. Results should be verified before use in any critical application. View our Terms of Service for more information.
Need to convert to other time units?
View all Time conversions →What is a Hour and a Century?
The hour (symbol: h or hr) is a unit of time equal to 60 minutes, 3,600 seconds, or 1/24 of a day.
Official SI-derived definition: Since the second was redefined atomically in 1967, one hour equals exactly 3,600 seconds, where each second is 9,192,631,770 periods of caesium-133 radiation. Therefore:
- 1 hour = 3,600 × 9,192,631,770 = 33,074,688,259,200,000 caesium-133 oscillations
- This equals approximately 33.07 quadrillion atomic oscillations
Practical conversions:
- 1 hour = 60 minutes (exact)
- 1 hour = 3,600 seconds (exact)
- 1 day = 24 hours (exact)
- 1 week = 168 hours (7 × 24)
- 1 year (365 days) = 8,760 hours (365 × 24)
The hour is not an SI base unit, but it is accepted for use with the SI due to its fundamental role in civil timekeeping and global coordination.
The 24-Hour Day
The division of the day into 24 hours reflects both astronomical reality and historical convention:
Astronomical basis:
- Earth rotates 360° in ~24 hours (one solar day)
- Each hour = 15° of rotation (360° ÷ 24 = 15°)
- This is why time zones are spaced ~15° longitude apart
- Solar noon occurs when the sun crosses the meridian (highest point)
Why 24, not 20 or 10?
- Ancient Egyptians used base-12 counting (duodecimal)
- 12 is highly divisible: factors are 1, 2, 3, 4, 6, 12
- 12 daytime hours + 12 nighttime hours = 24-hour cycle
- This system was inherited by Greeks, Romans, and eventually globally standardized
Solar vs. Sidereal Hours:
- Solar hour: Based on Earth's rotation relative to the Sun (24 hours per cycle)
- Sidereal hour: Based on Earth's rotation relative to distant stars (23 hours, 56 minutes, 4 seconds per cycle)
- Civil timekeeping uses solar hours because they align with day/night cycles
A century is a unit of time equal to 100 consecutive years. The word derives from Latin "centum" (one hundred).
Duration in Other Units
1 century equals:
- 100 years (exactly)
- 10 decades (100 ÷ 10)
- 1,200 months (100 × 12)
- ~5,217 weeks (100 × 52.17)
- 36,524 days (100 common years) or 36,525 days (accounting for ~25 leap years)
- Average: 36,525 days (100 × 365.25)
- 876,600 hours (36,525 × 24)
- 52,596,000 minutes (876,600 × 60)
- 3,155,760,000 seconds (52,596,000 × 60)
Century Boundaries: The 1 vs. 0 Debate
Formal reckoning (technically correct):
- 1st century: 1-100 CE
- 18th century: 1701-1800
- 19th century: 1801-1900
- 20th century: 1901-2000
- 21st century: 2001-2100
Why? Because there was no year 0 in the Gregorian calendar (1 BCE → 1 CE directly), the first century was years 1-100, not 0-99.
Popular usage (dominant in practice):
- 18th century: "The 1700s" (1700-1799)
- 19th century: "The 1800s" (1800-1899)
- 20th century: "The 1900s" (1900-1999)
- 21st century: "The 2000s onward" (2000-2099)
Reality: Popular usage dominates. When people say "20th century," they typically mean 1900-1999, not 1901-2000. The millennium celebration happened January 1, 2000, not January 1, 2001, despite formal correctness.
Note: The Hour is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Century belongs to the imperial/US customary system.
History of the Hour and Century
of the Hour
Ancient Egyptian Origins (c. 2000 BCE)
The earliest systematic division of day and night into hours comes from ancient Egypt around 2000 BCE. Egyptian priests needed to schedule temple rituals and religious observations throughout the day and night.
Egyptian timekeeping innovations:
-
Shadow clocks (sundials): Used during daylight to track time by shadow position
- Divided daylight into 12 parts
- Earliest example: Obelisk shadow clock (c. 1500 BCE)
-
Water clocks (clepsydrae): Used at night and cloudy days
- Water dripped from container at constant rate
- Markings indicated elapsed time
- Divided nighttime into 12 parts
Crucial limitation: Seasonal hours (temporales horae)
- Summer daylight hours were longer than winter daylight hours
- Example: In Egypt, summer daytime hour ≈ 75 minutes, winter daytime hour ≈ 45 minutes
- Nighttime hours varied inversely (longer in winter, shorter in summer)
- This made sense for agricultural societies organized around daylight availability
Why 12 divisions?
- Egyptians used base-12 (duodecimal) counting, possibly because:
- 12 lunar months per year
- 12 knuckles on four fingers (excluding thumb)—convenient finger counting
- 12 is highly divisible (1, 2, 3, 4, 6, 12)
Greek and Roman Refinement (300 BCE - 400 CE)
Hellenistic astronomers (c. 300 BCE) introduced the concept of equal-length hours:
- "Equinoctial hours": Dividing the full 24-hour day-night cycle into 24 equal parts
- Each equinoctial hour = 1/24 of a mean solar day
- This was primarily used for astronomical calculations, not daily timekeeping
- Hipparchus (c. 150 BCE) used equinoctial hours for celestial observations
Roman timekeeping:
- Romans continued using seasonal hours for daily life
- Day (from sunrise to sunset) divided into 12 horae
- Night divided into 4 vigiliae (watches) of 3 hours each
- "First hour" (prima hora) = first hour after sunrise (varies by season)
- "Sixth hour" (sexta hora) = midday → origin of "siesta"
- "Eleventh hour" = last hour before sunset → modern idiom "at the eleventh hour" (last minute)
Roman water clocks (clepsydrae):
- Public water clocks in marketplaces
- Adjusted seasonally to maintain 12-hour daytime divisions
- Used for timing speeches in Senate (each senator allotted specific time)
Medieval Islamic Golden Age (700-1300 CE)
Islamic scholars made critical advances in precise timekeeping for astronomical observations and prayer time calculations:
Five daily prayers (salat):
- Fajr (dawn), Dhuhr (midday), Asr (afternoon), Maghrib (sunset), Isha (evening)
- Required accurate determination of solar positions
- Drove development of sophisticated astronomical clocks
Key innovations:
- Astronomical tables (zij): Calculated prayer times using equinoctial hours
- Astrolabes: Portable astronomical computers for time determination
- Advanced water clocks: Al-Jazari's "Castle Clock" (1206) featured complex automata
- Mathematical timekeeping: Used trigonometry to calculate hour angles
Islamic astronomers fully adopted equinoctial hours for scientific work while society continued using seasonal hours for daily activities.
Mechanical Clocks and Hour Standardization (1300-1600)
The invention of mechanical clocks in medieval Europe around 1280-1300 CE forced the adoption of equal-length hours:
Why mechanical clocks standardized hours:
- Mechanical escapement mechanisms tick at constant rates
- Cannot automatically adjust for seasonal variations
- Fixed 24-hour cycle physically built into clockwork
- This made equal-length hours the practical default
Early public clocks:
- Salisbury Cathedral Clock (England, c. 1386): Still running, one of oldest
- Wells Cathedral Clock (England, c. 1390): Features astronomical dial
- Prague Astronomical Clock (Czech Republic, 1410): Shows multiple time systems
- Church tower clocks visible/audible across towns
- Bells chimed on the hour, coordinating community activities
Impact on society:
- Transition from "task-oriented time" (work until task done) to "clock time" (work specific hours)
- Monasteries first adopted strict hour-based schedules (canonical hours)
- Urban merchants and craftsmen followed
- "Time discipline" emerged: punctuality became valued
Hour angles and navigation:
- 1 hour = 15° longitude (since Earth rotates 360° in 24 hours)
- Ships could determine longitude by comparing local solar noon to chronometer showing home port time
- This principle drove development of marine chronometers in 1700s
12-Hour vs. 24-Hour Time Notation
12-hour clock (with AM/PM):
- AM = ante meridiem (Latin: before midday)
- PM = post meridiem (Latin: after midday)
- Hours: 12:00 AM (midnight), 1 AM-11 AM, 12:00 PM (noon), 1 PM-11 PM
- Used in: United States, Canada, Australia, Philippines, parts of Latin America
- Ambiguity issue: 12:00 AM vs. 12:00 PM frequently confused
24-hour clock (military time):
- Hours numbered 00:00 (midnight) through 23:59
- Used in: Most of Europe, Asia, Africa, South America, military/aviation worldwide
- ISO 8601 international standard: HH:MM:SS format (e.g., 14:30:00)
- Eliminates AM/PM ambiguity
- Preferred for timetables, logistics, computing
Historical development:
- Ancient Egyptians and Romans used 1-12 numbering twice daily
- 24-hour notation emerged with astronomical use in Renaissance
- Military adoption (especially WWI era) standardized 24-hour format
- Computing systems use 24-hour format internally
Time Zones: Dividing Earth into Hours (1883-1884)
Before the late 1800s, each town kept its own "local solar time" based on the sun's position. This created chaos for railroad timetables—a train journey might cross dozens of different local times.
Railroad time standardization (1883):
- US/Canadian railroads established four continental time zones on November 18, 1883
- Each zone spanned roughly 15° longitude (one hour)
- Cities synchronized clocks within each zone
International Meridian Conference (1884, Washington D.C.):
- Established Greenwich, England as 0° longitude (Prime Meridian)
- Divided Earth into 24 standard time zones, each 15° wide
- Each zone offset by one hour from UTC (Coordinated Universal Time, formerly GMT)
- Created International Date Line at 180° longitude
Modern time zones:
- Standard zones: UTC-12 to UTC+14 (some zones offset by 30 or 45 minutes)
- Daylight Saving Time: Advances clocks 1 hour in summer in some regions
- Political boundaries: Zones follow country borders, not just longitude
- China uses single time zone (UTC+8) despite spanning 5 geographical zones
Atomic Era: Hours Defined by Seconds (1967-Present)
When the second was redefined atomically in 1967 based on caesium-133 oscillations, the hour inherited this precision:
1 hour = exactly 3,600 SI seconds = 33,074,688,259,200,000 caesium oscillations
Modern atomic clocks maintain this definition with extraordinary stability:
- Caesium fountain clocks: Accurate to 1 second in 100 million years
- Optical lattice clocks: Accurate to 1 second in 15 billion years (2019)
- GPS satellites: Each carries atomic clocks synchronized to nanoseconds
Leap seconds:
- Earth's rotation gradually slows (tidal friction)
- Occasionally, an extra second added to clock time to match Earth rotation
- 27 leap seconds added 1972-2016
- Controversy: May be abolished in favor of "leap hours" every few centuries
of the Century Concept
1. Ancient Origins: Roman Centuria (509 BCE - 27 BCE)
Roman military organization:
- Centuria (plural: centuriae) = Roman military unit of approximately 100 soldiers (later reduced to 80)
- Led by a centurion (centurio)
- Latin "centum" = one hundred
- 6 centuries = 1 cohort; 10 cohorts = 1 legion (~6,000 soldiers)
Early timekeeping:
- Romans used Ab urbe condita (AUC, "from the founding of the city") dating from Rome's legendary founding (753 BCE)
- No systematic use of "century" for 100-year periods yet
- Time organized by consulships, reigns, dynasties
2. Calendar Development and Anno Domini Dating (1 CE - 1582 CE)
Anno Domini (AD) system:
- Dionysius Exiguus (c. 525 CE): Calculated years from Jesus Christ's birth
- Introduced Anno Domini (AD, "in the year of the Lord") dating
- Critical error: No year 0 (went directly from 1 BCE to 1 CE)
- This creates century boundary confusion still debated today
Julian Calendar (46 BCE - 1582 CE):
- Julius Caesar introduced 365.25-day year (leap year every 4 years)
- Provided stable framework for long-term chronology
- Enabled systematic dating of events over centuries
Gregorian Calendar Reform (1582 CE):
- Pope Gregory XIII corrected Julian calendar drift
- Established modern calendar system still used today
- Removed 10 days (October 4, 1582 → October 15, 1582)
- Century years divisible by 400 are leap years (1600, 2000), others not (1700, 1800, 1900)
3. Renaissance and Enlightenment: Historical Periodization (1400s-1700s)
Systematic historiography emerged:
- 15th-16th centuries: Renaissance scholars developed historical chronologies
- 17th-18th centuries: Enlightenment historians systematized century-based periodization
- Edward Gibbon (Decline and Fall of the Roman Empire, 1776-1789): Used century-scale analysis
Why centuries became standard:
- Generational scale: ~4 generations per century = intergenerational change visible but comprehensible
- Administrative records: Tax records, census data, government documents accumulated over centuries
- Pattern recognition: 100-year scale reveals structural changes invisible in decade-scale analysis
- Round number psychology: Base-10 counting makes 100-year periods psychologically satisfying
Periodization labels emerged:
- "The 16th century" = 1500s Renaissance, Reformation
- "The 17th century" = 1600s Scientific Revolution, Baroque
- "The 18th century" = 1700s Age of Enlightenment, Industrial Revolution begins
4. 19th Century: Century as Historical Framework (1801-1900)
The "long 19th century" concept:
- Historians sometimes define as 1789-1914 (French Revolution to WWI)
- Captures coherent historical era despite not matching formal century boundaries
Major 19th-century transformations:
- Industrial Revolution (1760-1840): Steam power, factories, railroads
- Urbanization: Rural → urban population shift
- Imperialism: European colonial empires peak
- Scientific progress: Darwin, Maxwell, Mendel
- Political revolutions: 1848 Revolutions, unification of Germany/Italy
- Technological: Telegraph, telephone, photography, electricity
Century consciousness:
- People in 1800s increasingly thought in century-scale terms
- "The spirit of the 19th century" = common phrase
- Fin de siècle (end of century, 1890s-1900s) = cultural movement
5. 20th Century: Century of Extremes (1901-2000)
Eric Hobsbawm's "short 20th century" (1914-1991):
- WWI start to Soviet Union collapse
- Captures coherent historical narrative despite formal century boundaries
Major 20th-century transformations:
- World Wars: WWI (1914-1918), WWII (1939-1945)
- Ideological conflict: Fascism, Communism, Capitalism compete
- Cold War (1947-1991): US vs. USSR, nuclear arms race
- Decolonization: European empires disintegrate (1940s-1970s)
- Technological revolutions:
- Automobiles, airplanes (early 1900s)
- Nuclear energy (1940s)
- Computers (1940s-1950s)
- Space exploration (1950s-1960s)
- Internet (1990s)
- Mobile phones (1990s-2000s)
- Population explosion: 1.6 billion (1900) → 6.1 billion (2000)
- Medical advances: Antibiotics, vaccines, life expectancy doubled
- Environmental: Climate change, ozone depletion, biodiversity loss
Century labeling:
- "The American Century" (Henry Luce, 1941): US dominance of 20th century
- "The People's Century" (BBC, 1995): Mass politics, democracy spread
6. 21st Century: Digital Age and Beyond (2001-Present)
Millennium transition debate:
- Popular celebration: January 1, 2000 (Y2K)
- Formal start: January 1, 2001
- Most people celebrated 2000 despite pedantic correctness
21st-century defining features (so far):
- 9/11 attacks (2001): "War on Terror" begins
- Digital revolution: Smartphones ubiquitous (iPhone 2007)
- Social media: Facebook, Twitter, Instagram, TikTok
- Climate crisis: Accelerating global warming, extreme weather
- COVID-19 pandemic (2020-2023): Global disruption
- AI revolution: ChatGPT (2022), generative AI breakthroughs
- Geopolitical shifts: Rise of China, multipolar world
- Economic: 2008 Financial Crisis, wealth inequality
"21st-century skills": Digital literacy, critical thinking, adaptability
Common Uses and Applications: hours vs centuries
Explore the typical applications for both Hour (imperial/US) and Century (imperial/US) to understand their common contexts.
Common Uses for hours
and Applications
1. Time Zones and Global Coordination
The hour is the basis for global time coordination:
-
UTC (Coordinated Universal Time):
- Global time standard (replaced GMT in 1960s)
- Based on atomic clocks
- All time zones expressed as UTC offset
-
Major time zones:
- EST (Eastern Standard Time): UTC-5
- CST (Central Standard Time): UTC-6
- MST (Mountain Standard Time): UTC-7
- PST (Pacific Standard Time): UTC-8
- GMT/WET (Western European Time): UTC+0
- CET (Central European Time): UTC+1
- IST (Indian Standard Time): UTC+5:30
- JST (Japan Standard Time): UTC+9
- AEST (Australian Eastern Standard Time): UTC+10
-
Business hours across zones:
- "9 AM EST / 6 AM PST" (3-hour difference)
- International meetings: Finding overlapping work hours
- "Follow the sun" support: 24-hour coverage across global offices
-
International Date Line:
- 180° longitude (opposite side of Earth from Prime Meridian)
- Crossing eastward: Lose one day (skip 24 hours forward)
- Crossing westward: Gain one day (repeat 24 hours)
2. Scheduling and Calendar Systems
Hours are the building blocks of schedules:
-
Digital calendars:
- Google Calendar, Outlook: Default 1-hour event blocks
- Day view: Shows 24 hours (or work hours only)
- Week view: 168 hours (7 × 24)
- Buffer time: 15-30 minutes between hour blocks
-
Appointment systems:
- Medical: 15-minute to 1-hour slots
- Salon/spa: 30 minutes to 3 hours
- Professional meetings: 30-minute or 1-hour default
-
Business hours:
- Standard: 9 AM - 5 PM (8 hours, often called "9-to-5")
- Extended: 8 AM - 6 PM (10 hours)
- 24/7 operations: Open all 24 hours, 7 days per week
-
Peak hours vs. off-peak:
- Rush hour: 7-9 AM, 4-7 PM (commute times)
- Electricity pricing: Higher rates during peak demand hours
- Gym: Busiest 5-7 PM (post-work)
3. Astronomy and Earth Science
The hour reflects Earth's rotation:
-
Earth's rotation:
- 360° in ~24 hours = 15° per hour
- Solar noon: Sun crosses local meridian (highest point in sky)
- Local solar time: Based on sun position (varies with longitude)
- Mean solar time: Averaged over year (accounts for orbital eccentricity)
-
Equation of time:
- Sundial time vs. clock time can differ by ±16 minutes
- Due to Earth's elliptical orbit and axial tilt
- Clock time is averaged over the year
-
Hour angle (astronomy):
- Angular distance (in hours) from local meridian
- 1 hour = 15° of celestial sphere rotation
- Used to determine star positions for telescope pointing
-
Sidereal vs. solar day:
- Sidereal day: 23 hours 56 minutes 4 seconds (rotation relative to stars)
- Solar day: 24 hours (rotation relative to sun)
- Difference: Earth moves along orbit, sun appears to shift ~1° per day
4. Energy and Power Consumption
Energy usage measured in watt-hours:
-
Kilowatt-hour (kWh):
- Energy used by 1 kilowatt (1,000 watts) running for 1 hour
- Standard unit for electricity billing
- Average US home: 30 kWh per day (877 kWh per month)
-
Appliance energy use:
- 100W light bulb for 10 hours = 1 kWh
- Electric oven: 2-3 kWh per hour of use
- Central AC: 3-5 kWh per hour
- Laptop: 0.05 kWh per hour (50 watts)
- Refrigerator: 1-2 kWh per day (constant running)
-
Time-of-use pricing:
- On-peak hours: Higher electricity rates (typically 1-9 PM)
- Off-peak hours: Lower rates (typically 9 PM - 9 AM)
- Encourages load shifting to flatten demand curve
-
Battery capacity:
- Milliamp-hour (mAh) or watt-hour (Wh)
- Phone battery: 3,000 mAh (11 Wh) ≈ 2-3 hours screen-on time
- Laptop battery: 50-100 Wh ≈ 5-10 hours use
- Electric car: 60-100 kWh ≈ 250-400 miles range
5. Healthcare and Medicine
Medical dosing and monitoring uses hours:
-
Medication schedules:
- "Every 4 hours" = 6 times per day
- "Every 6 hours" = 4 times per day (QID: quater in die)
- "Every 8 hours" = 3 times per day (TID: ter in die)
- "Every 12 hours" = 2 times per day (BID: bis in die)
- "Every 24 hours" = 1 time per day (QD: quaque die)
-
Drug half-life:
- Time for drug concentration to decrease by half
- Acetaminophen: 2-3 hours
- Caffeine: 5-6 hours
- Alcohol: Eliminated at ~0.015% BAC per hour
-
Fasting requirements:
- Pre-surgery: 8-12 hours fasting (NPO: nil per os)
- Cholesterol test: 9-12 hours fasting
- Glucose tolerance test: 8-hour overnight fast
-
Labor and delivery:
- Labor stages measured in hours
- First stage: 6-12 hours (first baby), 4-8 hours (subsequent)
- Active labor: Cervical dilation ~1 cm per hour
- Pushing stage: 1-3 hours (first baby), 15 min-2 hours (subsequent)
-
Medical shift lengths:
- Resident work-hour restrictions: Max 80 hours per week, max 24-hour shifts
- Nurse shifts: Typically 8 or 12 hours
- Concerns about fatigue and patient safety
6. Computing and Technology
Hours measure uptime and usage:
-
Server uptime:
- "Five nines" (99.999%): 5.26 minutes downtime per year
- "Four nines" (99.99%): 52.6 minutes downtime per year
- "Three nines" (99.9%): 8.77 hours downtime per year
- Measured in hours of continuous operation
-
Data retention:
- Backup schedules: Hourly, daily, weekly
- Log rotation: Every 24 hours (daily logs)
- Cloud storage: Deleted items retained 30 days (720 hours)
-
Usage tracking:
- Screen time: Hours per day on devices
- YouTube Creator Studio: Watch hours (4,000 hours past year for monetization)
- Video games: "Hours played" stat
- Social media: "You've been using this app for 2 hours today"
-
Rendering and processing:
- Video rendering: "2 hours to render 10-minute 4K video"
- 3D modeling: "12-hour render time for scene"
- Machine learning training: "Training took 100 GPU-hours"
7. Legal and Regulatory
Many laws reference hours:
-
Work hour regulations:
- Fair Labor Standards Act (FLSA): 40-hour work week threshold
- Overtime pay: Time-and-a-half for hours beyond 40/week
- Maximum driving hours: Truckers limited to 11 hours driving per 14-hour window
-
Alcohol service hours:
- Many states prohibit alcohol sales certain hours (e.g., 2 AM - 6 AM)
- "Last call": Final hour for ordering drinks
-
Quiet hours:
- Residential noise ordinances: Often 10 PM - 7 AM
- College dorms: 11 PM - 8 AM weeknights
-
Statute of limitations:
- Measured in years, but technically hours
- Parking tickets: Often 72-hour (3-day) payment window
- Right to return/refund: 24-48 hour windows
When to Use centuries
and Applications
1. Historical Analysis and Research
Century-by-century comparison:
- Economic growth: "19th-century industrialization vs. 20th-century information age"
- Warfare evolution: "19th-century muskets → 20th-century machine guns → 21st-century drones"
- Life expectancy trends: Analyzed century-by-century
Academic papers:
- "This study examines voting patterns across two centuries (1800s-1900s)"
- "Century-scale climate reconstructions"
2. Art, Literature, and Cultural Studies
Periodization:
- "18th-century literature": Age of Enlightenment, Voltaire, Swift, Johnson
- "19th-century novel": Dickens, Austen, Tolstoy, Dostoevsky
- "20th-century art": Impressionism, Cubism, Surrealism, Abstract Expressionism
Art history courses: Often organized by century ("Art of the 17th Century")
3. Genealogy and Family History
Tracing ancestry:
- 4-5 generations per century = century scale ideal for family trees
- "My great-great-grandfather lived in the 19th century"
- Immigration records, census data organized by century
Life stages across centuries:
- Born late 1800s, died mid-1900s = lived through two centuries
4. Climate and Environmental Science
Century-scale climate patterns:
- Medieval Warm Period (10th-13th centuries): Warmer than average
- Little Ice Age (14th-19th centuries): Cooler than average
- 20th-21st century warming: Anthropogenic climate change
Projections:
- "By end of 21st century, sea level rise 1-2 meters"
5. Economic and Development Studies
Long-term economic trends:
- 19th century: Agricultural → industrial economies
- 20th century: Industrial → service/information economies
- 21st century: Digital/knowledge economies
Development indicators: Tracked over centuries (literacy, GDP, poverty)
6. Philosophy and Long-Term Thinking
"Think in centuries":
- Long Now Foundation: 10,000-year thinking
- Contrast with short-term thinking (quarterly earnings, election cycles)
Philosophical movements:
- 18th century: Enlightenment rationalism
- 19th century: Romanticism, existentialism emerges
- 20th century: Postmodernism
7. Legal and Property Rights
Land ownership records:
- Property deeds reference century-old transactions
- "Century farms": Farms in same family 100+ years
Copyright:
- Life + 70 years = often extends into next century after author's death
Additional Unit Information
About Hour (h)
How many minutes are in an hour?
Exactly 60 minutes. This comes from the ancient Babylonian base-60 (sexagesimal) number system, which the Egyptians and Greeks adopted for dividing hours. The Latin term "pars minuta prima" (first small part) referred to the first 60-part division of an hour, giving us the modern "minute."
How many seconds are in an hour?
Exactly 3,600 seconds (60 minutes × 60 seconds).
Since 1967, when the second was redefined using atomic caesium-133 clocks, one hour equals:
- 3,600 atomic seconds
- 33,074,688,259,200,000 caesium-133 oscillations (33.07 quadrillion)
This makes the hour one of the most precisely defined units of time in existence.
How many hours are in a day?
Exactly 24 hours in one solar day.
Why 24?
- Ancient Egyptians divided day and night into 12 parts each
- 12 + 12 = 24-hour cycle
- Earth rotates 360° in 24 hours = 15° per hour
- This 15° per hour relationship forms the basis for time zones
Note: A sidereal day (rotation relative to stars) is 23 hours, 56 minutes, 4 seconds, but civil timekeeping uses the 24-hour solar day (rotation relative to the sun).
How many hours are in a year?
8,760 hours in a standard 365-day year.
Calculation: 365 days × 24 hours = 8,760 hours
For a leap year (366 days): 8,784 hours (24 more hours).
Work year: Assuming 40-hour weeks and 52 weeks, a full-time work year is 2,080 work hours (not including holidays or vacation).
Why do we use 12-hour AM/PM instead of 24-hour time?
Historical reasons:
- Ancient Egyptians and Romans divided day and night into 12 parts each
- This became culturally entrenched in English-speaking countries
- 12-hour clocks were simpler to manufacture (only need 1-12 markers)
Why 24-hour format exists:
- Eliminates AM/PM confusion (especially 12:00 AM vs. 12:00 PM)
- Preferred in military, aviation, healthcare, computing for clarity
- Standard in most non-English-speaking countries
- ISO 8601 international standard uses 24-hour format
Current usage:
- 12-hour: US, Canada, Australia, Philippines, parts of UK
- 24-hour: Most of Europe, Asia, Africa, South America, military worldwide
What's the difference between a 24-hour day and Earth's rotation?
Solar day (24 hours): Time for sun to return to same position in sky Sidereal day (23h 56m 4s): Time for Earth to rotate 360° relative to distant stars
Why the difference?
- Earth orbits the sun while rotating
- After one 360° rotation, Earth has moved ~1° along its orbit
- Must rotate an additional ~1° (4 minutes) for sun to return to same position
- 365.25 solar days per year, but 366.25 sidereal days per year (one extra rotation)
Practical impact:
- Astronomers use sidereal time for telescope pointing
- Civil timekeeping uses solar time (24-hour day)
- Stars rise ~4 minutes earlier each day (sidereal effect)
How do Daylight Saving Time changes work?
Spring forward (start of DST):
- Clocks advance 1 hour at 2:00 AM → becomes 3:00 AM
- The hour from 2:00-3:00 AM doesn't exist that day
- Day has only 23 hours
- "Lose an hour of sleep"
Fall back (end of DST):
- Clocks retreat 1 hour at 2:00 AM → becomes 1:00 AM again
- The hour from 1:00-2:00 AM occurs twice
- Day has 25 hours
- "Gain an hour of sleep"
Global variation:
- Northern Hemisphere: Starts March/April, ends October/November
- Southern Hemisphere: Starts September/October, ends March/April
- Many countries don't observe DST (China, Japan, India, most of Africa)
- Arizona and Hawaii (US states) don't observe DST
Controversy: Growing movement to abolish DST due to health impacts, minimal energy savings.
Why are time zones roughly 15 degrees wide?
Simple math:
- Earth rotates 360° in 24 hours
- 360° ÷ 24 hours = 15° per hour
- Each time zone theoretically spans 15° longitude
Reality is messier:
- Political boundaries: Zones follow country/state borders
- China uses single time zone (UTC+8) despite spanning 60° longitude (5 theoretical zones)
- India uses UTC+5:30 (half-hour offset from standard)
- Some zones are 30 or 45-minute offsets (Nepal: UTC+5:45)
Practical example:
- Greenwich, England: 0° longitude (Prime Meridian)
- Every 15° east: Add 1 hour (15°E = UTC+1, 30°E = UTC+2, etc.)
- Every 15° west: Subtract 1 hour (15°W = UTC-1, 30°W = UTC-2, etc.)
What is a "billable hour"?
A billable hour is time spent on client work that can be charged to the client, common in legal, consulting, and professional services.
How it works:
- Professionals track time in increments (often 6 minutes = 0.1 hour)
- Multiply hours by hourly rate
- Example: 7.5 billable hours × $300/hour = $2,250
Billing increment examples:
- 6 minutes = 0.1 hour (common in legal)
- 15 minutes = 0.25 hour (quarter-hour)
- Some firms round up to nearest increment
Utilization rate:
- Target: 1,500-2,000 billable hours per year (out of 2,080 work hours)
- Remaining time: Non-billable (admin, business development, training)
- 75-80% utilization considered good in many professions
Ethical concerns:
- Pressure to inflate hours
- Some professions moving to flat-fee or value-based pricing
Can an hour ever be longer or shorter than 60 minutes?
In standard timekeeping: No. An hour is always exactly 60 minutes or 3,600 seconds.
Exceptions and special cases:
-
Leap seconds:
- Very rarely, an extra second added to last minute of day
- Makes that minute 61 seconds, but hour still 3,600 seconds overall
- Last hour of day becomes 3,601 seconds
- 27 leap seconds added 1972-2016
-
Daylight Saving Time transitions:
- "Spring forward": The 2:00 AM hour is skipped (day has 23 hours)
- "Fall back": The 1:00 AM hour occurs twice (day has 25 hours)
- This affects the day length, not individual hour length
-
Historical seasonal hours:
- Ancient/medieval timekeeping used "unequal hours"
- Summer daylight hour ≈ 75 minutes
- Winter daylight hour ≈ 45 minutes
- Obsolete since mechanical clocks standardized equal hours
Future possibility:
- If leap seconds abolished, may use "leap hours" every few centuries instead
Why is rush hour called an "hour" when it lasts 2-3 hours?
Etymology: "Rush hour" originally referred to the peak single hour of commuter traffic, but the term stuck even as traffic congestion expanded.
Modern reality:
- Morning rush: 7:00-9:00 AM (2-3 hours)
- Evening rush: 4:00-7:00 PM (3-4 hours)
- Can extend longer in major cities
Related terms:
- "Peak hours": Broader term for high-traffic periods
- "Congestion pricing": Charging more during rush hours to reduce traffic
- "Off-peak": Outside rush hours, usually smoother travel
Cultural note: The term persists despite inaccuracy, similar to how we still say "dial a phone" or "roll down the window."
About Century (c)
1. How many years are in a century?
Exactly 100 years. The word "century" comes from Latin "centum" (one hundred).
Other units:
- 1 century = 100 years = 10 decades = 1,200 months = ~36,525 days
2. When did the 21st century begin?
Formal answer: January 1, 2001 (because there was no year 0, the 1st century was years 1-100, so the 21st century is 2001-2100).
Popular answer: January 1, 2000 (most people celebrated the new millennium in 2000, and colloquially refer to "the 2000s" as the start of the 21st century).
Reality: Both are used; formal definition is technically correct, but popular usage dominates in practice.
3. Why is the 1800s called the 19th century?
Because of how centuries are numbered:
- 1st century = years 1-100
- 2nd century = years 101-200
- 18th century = years 1701-1800
- 19th century = years 1801-1900 (the "1800s")
- 20th century = years 1901-2000 (the "1900s")
Rule: Century number = (hundreds digit + 1). So 1800s → century 18+1 = 19th century.
4. How many generations are in a century?
Approximately 4-5 generations, assuming ~20-25 years per generation.
Calculation:
- If generation = 25 years → 100 ÷ 25 = 4 generations per century
- If generation = 20 years → 100 ÷ 20 = 5 generations per century
Example: Great-great-grandparents often lived in a different century than you.
5. Is a century a standard unit in science?
No. The century is not part of the International System of Units (SI). The SI base unit for time is the second.
Scientific time units:
- Years (Julian year = 365.25 days exactly)
- Kiloyears (kyr): 1,000 years
- Megayears (Myr): 1,000,000 years
- Gigayears (Gyr): 1,000,000,000 years
Century usage: Common in history, demography, climate science, but not formal SI unit.
6. How many days are in a century?
Approximately 36,525 days (accounting for leap years).
Calculation:
- 100 years × 365 days = 36,500 days
- Plus ~25 leap days per century = 36,525 days total
Exact number varies: Depends on leap year distribution (Gregorian calendar: 97 leap years per 400 years).
7. What is the difference between centennial and bicentennial?
Centennial: 100th anniversary (1 century)
Bicentennial: 200th anniversary (2 centuries)
Other -ennial terms:
- Sesquicentennial: 150th anniversary (1.5 centuries)
- Tercentennial/Tricentennial: 300th anniversary (3 centuries)
- Quadricentennial: 400th anniversary (4 centuries)
- Quincentennial: 500th anniversary (5 centuries)
8. Can a person live in three different centuries?
Yes, but extremely rare.
Requirements:
- Born in one century (e.g., 1898, 19th century)
- Live through next century (1900s, 20th century)
- Live into third century (2000s, 21st century)
- Requires living 102+ years if born in last years of century
Example: Born December 1898 (19th century) → lived through 20th century (1901-2000) → died January 2001 (21st century) = lived in 3 centuries despite being only 102 years old.
9. What is a "long century" in history?
Historical concept: Period longer than 100 years but representing a coherent historical era.
Famous examples:
- "Long 19th century" (1789-1914): French Revolution to WWI start
- "Long 18th century" (1688-1815): Glorious Revolution to Waterloo
- "Short 20th century" (1914-1991): Conversely, WWI to USSR collapse = only 77 years but captures coherent era
Why useful: Historical eras don't align neatly with formal century boundaries; "long/short century" captures thematic unity.
10. How do I calculate how many centuries between two years?
Formula: centuries = (ending year - starting year) ÷ 100
Examples:
- 1500 to 2000: (2000 - 1500) ÷ 100 = 5 centuries (500 years)
- 1776 to 2024: (2024 - 1776) ÷ 100 = 2.48 centuries (~248 years)
- 1900 to 2100: (2100 - 1900) ÷ 100 = 2 centuries (200 years)
11. What is "fin de siècle"?
French phrase: "End of the century" (literally "end of era")
Historical meaning: Cultural period at end of 19th century (1890s-1900s) characterized by:
- Cultural pessimism mixed with optimism
- Decadence, Art Nouveau
- Anxiety about modernity
- Transition into new century
Modern usage: Any "end of century" cultural moment (Y2K was modern "fin de siècle").
12. How many centuries in a millennium?
10 centuries = 1 millennium
Conversions:
- 1 century = 0.1 millennia (100 years)
- 5 centuries = 0.5 millennia (500 years)
- 10 centuries = 1 millennium (1,000 years)
- 20 centuries = 2 millennia (2,000 years)
Conversion Table: Hour to Century
| Hour (h) | Century (c) |
|---|---|
| 0.5 | 0 |
| 1 | 0 |
| 1.5 | 0 |
| 2 | 0 |
| 5 | 0 |
| 10 | 0 |
| 25 | 0 |
| 50 | 0 |
| 100 | 0 |
| 250 | 0 |
| 500 | 0.001 |
| 1,000 | 0.001 |
People Also Ask
How do I convert Hour to Century?
To convert Hour to Century, enter the value in Hour in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our time converter page to convert between other units in this category.
Learn more →What is the conversion factor from Hour to Century?
The conversion factor depends on the specific relationship between Hour and Century. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.
Can I convert Century back to Hour?
Yes! You can easily convert Century back to Hour by using the swap button (⇌) in the calculator above, or by visiting our Century to Hour converter page. You can also explore other time conversions on our category page.
Learn more →What are common uses for Hour and Century?
Hour and Century are both standard units used in time measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our time converter for more conversion options.
For more time conversion questions, visit our FAQ page or explore our conversion guides.
Helpful Conversion Guides
Learn more about unit conversion with our comprehensive guides:
All Time Conversions
Other Time Units and Conversions
Explore other time units and their conversion options:
Verified Against Authority Standards
All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.
National Institute of Standards and Technology — Official time standards and definitions
Bureau International des Poids et Mesures — Definition of the SI base unit for time
Last verified: December 3, 2025