Temperature Unit Converter

Quick Start: Temperature Conversions

Convert between Celsius, Fahrenheit, and Kelvin instantly. Perfect for weather forecasts, cooking recipes, scientific research, and international travel.

Most Popular Conversions:

• Celsius to Fahrenheit - Weather & travel
• Fahrenheit to Celsius - International weather
• Celsius to Kelvin - Scientific calculations
• Kelvin to Celsius - Lab measurements
• Fahrenheit to Kelvin - Physics problems

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Understanding Temperature Conversions

Temperature measures the degree of hotness or coldness of an object or environment. Understanding how to convert between different temperature scales is crucial in science, cooking, weather forecasting, and international communication.

Why Temperature Conversion Matters

Weather & Travel: Weather forecasts in Europe show Celsius while US displays Fahrenheit. Understanding both helps interpret conditions when traveling internationally.

Cooking & Baking: Recipes from different countries use different scales. Oven temperatures must be converted accurately—a 25°F error can ruin baked goods.

Scientific Research: Scientists worldwide use Kelvin for absolute temperature measurements and Celsius for practical applications. Research papers require accurate conversions.

Medical & Health: Body temperature, fever thresholds, and medication storage temperatures vary by region. Knowing both scales ensures proper health monitoring.

HVAC & Climate Control: Thermostats, air conditioning specifications, and heating systems use region-specific scales requiring conversion for international equipment.

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Common Temperature Scales Explained

Celsius (°C) - International Standard

Overview: The most widely used temperature scale globally, part of the metric system. Used by most countries for weather, cooking, and everyday measurements.

Key Points:

• Water freezes: 0°C
• Water boils: 100°C (at standard pressure)
• Room temperature: ~20-22°C
• Human body temperature: 37°C
• Developed by: Anders Celsius (1742)

Where used: Europe, Asia, Africa, South America, Australia, Canada, and most of the world.

Scale design: Based on water's phase transitions at sea level (0° freeze, 100° boil), divided into 100 equal degrees.

Fahrenheit (°F) - US Standard

Overview: Primary temperature scale in the United States, Cayman Islands, and some Caribbean nations. Offers finer granularity for everyday temperatures.

Key Points:

• Water freezes: 32°F
• Water boils: 212°F (at standard pressure)
• Room temperature: ~68-72°F
• Human body temperature: 98.6°F
• Developed by: Daniel Gabriel Fahrenheit (1724)

Where used: United States, US territories, Bahamas, Belize, Cayman Islands, Palau.

Scale design: Originally based on three fixed points: 0°F (brine freezing point), 32°F (water freezing), 96°F (estimated human body temperature, later revised to 98.6°F).

Kelvin (K) - Absolute Scientific Scale

Overview: The SI base unit for thermodynamic temperature, used in scientific research worldwide. An absolute scale starting at absolute zero (no thermal energy).

Key Points:

• Absolute zero: 0 K (coldest possible temperature)
• Water freezes: 273.15 K
• Water boils: 373.15 K (at standard pressure)
• Room temperature: ~293-295 K
• Human body temperature: 310 K
• Developed by: Lord Kelvin (William Thomson, 1848)

Where used: Physics, chemistry, astronomy, cryogenics, and all scientific research requiring absolute temperature measurements.

Scale design: Same increment size as Celsius (1 K = 1°C change), but starts at absolute zero. No negative values exist on the Kelvin scale.

Note: The degree symbol (°) is NOT used with Kelvin. Write "300 K" not "300°K".

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Conversion Formulas

Quick Reference

From	To	Formula
Celsius	Fahrenheit	°F = (°C × 9/5) + 32
Fahrenheit	Celsius	°C = (°F - 32) × 5/9
Celsius	Kelvin	K = °C + 273.15
Kelvin	Celsius	°C = K - 273.15
Fahrenheit	Kelvin	K = (°F - 32) × 5/9 + 273.15
Kelvin	Fahrenheit	°F = (K - 273.15) × 9/5 + 32

Detailed Conversion Examples

Celsius to Fahrenheit:

• 0°C: (0 × 1.8) + 32 = 32°F (freezing)
• 20°C: (20 × 1.8) + 32 = 68°F (room temp)
• 37°C: (37 × 1.8) + 32 = 98.6°F (body temp)
• 100°C: (100 × 1.8) + 32 = 212°F (boiling)

Fahrenheit to Celsius:

• 32°F: (32 - 32) × 0.556 = 0°C (freezing)
• 68°F: (68 - 32) × 0.556 = 20°C (room temp)
• 98.6°F: (98.6 - 32) × 0.556 = 37°C (body temp)
• 212°F: (212 - 32) × 0.556 = 100°C (boiling)

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Practical Temperature Examples

Weather & Climate

Cold Weather:

• -40°C/-40°F: Extreme cold (same in both scales!)
• -20°C/-4°F: Very cold winter day
• -10°C/14°F: Cold winter day
• 0°C/32°F: Freezing point of water
• 10°C/50°F: Cool spring/fall day

Moderate Weather:

• 15°C/59°F: Mild day, light jacket weather
• 20°C/68°F: Comfortable room temperature
• 25°C/77°F: Warm summer day
• 30°C/86°F: Hot summer day

Hot Weather:

• 35°C/95°F: Very hot day
• 40°C/104°F: Extreme heat
• 45°C/113°F: Dangerously hot (Death Valley records: 56.7°C/134°F)

Cooking Temperatures

Oven Settings:

• 150°C/300°F: Low/slow cooking
• 175°C/350°F: Standard baking temperature
• 200°C/400°F: Roasting vegetables
• 220°C/425°F: High-heat roasting
• 230°C/450°F: Pizza baking
• 260°C/500°F: Broiling

Food Safety:

• 63°C/145°F: Medium-rare beef (minimum safe)
• 71°C/160°F: Ground beef (fully cooked)
• 74°C/165°F: Chicken breast (safe minimum)
• 82°C/180°F: Pulled pork (ideal tenderness)
• 100°C/212°F: Boiling water for pasta

Science & Laboratory

Cryogenics:

• 0 K/-273.15°C/-459.67°F: Absolute zero
• 4 K/-269°C/-452°F: Liquid helium
• 77 K/-196°C/-321°F: Liquid nitrogen
• 90 K/-183°C/-297°F: Liquid oxygen

Common Lab Temperatures:

• 273.15 K/0°C/32°F: Ice point
• 293 K/20°C/68°F: Room temperature
• 310 K/37°C/98.6°F: Human body temp
• 373.15 K/100°C/212°F: Water boiling point

Space & Astronomy:

• 2.7 K: Cosmic microwave background
• 5,778 K: Sun's surface temperature
• 15 million K: Sun's core temperature

Medical & Health

Human Body:

• 35°C/95°F: Hypothermia begins
• 36.5-37.5°C/97.7-99.5°F: Normal body temperature range
• 37°C/98.6°F: Average body temperature
• 38°C/100.4°F: Low-grade fever
• 39°C/102°F: Moderate fever
• 40°C/104°F: High fever (seek medical attention)
• 42°C/107.6°F: Life-threatening hyperthermia

Medical Storage:

• -80°C/-112°F: Ultra-cold freezer (vaccines, samples)
• -20°C/-4°F: Standard freezer
• 2-8°C/36-46°F: Refrigerator (medication storage)
• 20-25°C/68-77°F: Room temperature storage

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Common Conversion Mistakes

Mistake 1: Forgetting to Add/Subtract 32

Error: Converting 20°C as "20 × 1.8 = 36°F" Correction: 20°C = (20 × 1.8) + 32 = 68°F. Always add 32 when converting C to F.

Mistake 2: Wrong Order of Operations

Error: Converting 68°F as "(68 × 5/9) - 32" Correction: Subtract 32 FIRST: (68 - 32) × 5/9 = 20°C. Order matters!

Mistake 3: Using Degree Symbol with Kelvin

Error: Writing "300°K" Correction: Write "300 K" (no degree symbol). Kelvin is an absolute scale, not measured in degrees.

Mistake 4: Confusing Kelvin Offset

Error: "0°C = 0 K" Correction: 0°C = 273.15 K. Kelvin is offset by 273.15, not zero.

Mistake 5: Rounding Too Early

Error: Using 273 instead of 273.15 for Kelvin conversions Correction: Use 273.15 for accuracy. The 0.15 difference matters in scientific calculations.

Mistake 6: Approximating 5/9 and 9/5

Error: Using "2" instead of 1.8 (9/5) for C to F conversion Correction: 9/5 = 1.8 exactly. Using 2 introduces 10% error.

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Frequently Asked Questions

How do I convert Celsius to Fahrenheit?

Formula: °F = (°C × 9/5) + 32 or °F = (°C × 1.8) + 32

Step by step:

1. Multiply Celsius temperature by 1.8 (or 9/5)
2. Add 32 to the result

Examples:

• 0°C: (0 × 1.8) + 32 = 32°F
• 20°C: (20 × 1.8) + 32 = 68°F
• 37°C: (37 × 1.8) + 32 = 98.6°F
• 100°C: (100 × 1.8) + 32 = 212°F

Quick mental math: Double the Celsius, subtract 10%, add 32

• 20°C: 20 × 2 = 40, minus 4 = 36, plus 32 = 68°F

Convert Celsius to Fahrenheit →

How do I convert Fahrenheit to Celsius?

Formula: °C = (°F - 32) × 5/9 or °C = (°F - 32) × 0.5556

Step by step:

1. Subtract 32 from Fahrenheit temperature
2. Multiply the result by 5/9 (or 0.5556)

Examples:

• 32°F: (32 - 32) × 0.5556 = 0°C
• 68°F: (68 - 32) × 0.5556 = 20°C
• 98.6°F: (98.6 - 32) × 0.5556 = 37°C
• 212°F: (212 - 32) × 0.5556 = 100°C

Quick mental math: Subtract 32, then halve the result (gives approximate value)

• 68°F: 68 - 32 = 36, ÷ 2 = 18°C (actual: 20°C)

Convert Fahrenheit to Celsius →

What is Kelvin and how does it relate to Celsius?

Kelvin (K) is an absolute temperature scale where 0 K is absolute zero—the coldest possible temperature where particles have minimal thermal motion.

Relationship to Celsius:

• Same increment size: 1 K = 1°C change
• Offset by 273.15: K = °C + 273.15
• No negative values in Kelvin

Key conversions:

• 0 K = -273.15°C (absolute zero)
• 273.15 K = 0°C (water freezes)
• 293 K = 20°C (room temperature)
• 373.15 K = 100°C (water boils)

Why use Kelvin?

• Required for thermodynamic calculations
• Avoids negative temperatures
• Directly proportional to thermal energy
• Universal scientific standard

Convert Celsius to Kelvin →

What is absolute zero?

Absolute zero is the theoretical lowest possible temperature: 0 K, -273.15°C, or -459.67°F.

At absolute zero, particles have minimal quantum mechanical motion (zero-point energy). Classical physics would predict complete stillness, but quantum mechanics requires some residual motion.

Key facts:

• Cannot be reached in practice (third law of thermodynamics)
• Closest achieved: 0.0000000001 K (100 picokelvin)
• At this temperature: gases become liquids/solids, superconductivity occurs
• Provides natural "zero" for Kelvin scale

Real-world cold temperatures:

• Liquid helium: 4 K (-269°C)
• Liquid nitrogen: 77 K (-196°C)
• Coldest natural spot on Earth: -89.2°C (Vostok, Antarctica)
• Coldest lab temperature: ~100 picokelvin

Why is Fahrenheit still used in the US?

Historical reasons:

• Fahrenheit scale predates Celsius (1724 vs 1742)
• US adopted it before Celsius gained prominence
• Established in education, infrastructure, daily life

Practical advantages (argued by proponents):

• Finer granularity: 180 degrees between freezing/boiling (vs 100 in Celsius)
• Weather scale 0-100°F roughly covers human comfort range
• Switching costs would be enormous (signs, equipment, education)

Current status:

• US remains one of few countries using Fahrenheit primarily
• Science and medicine in US use Celsius/Kelvin
• Some weather services show both scales

Comparison:

• Metric world: Most countries switched to Celsius in 1960s-1970s
• US: Attempted metrication in 1970s but public adoption failed
• Today: Dual labeling common on US products

Which temperature scale is primarily used in scientific research?

Kelvin (K) is the standard SI unit for temperature in scientific research, especially in:

• Physics (thermodynamics, statistical mechanics)
• Chemistry (reaction rates, equilibrium)
• Astronomy (stellar temperatures)
• Cryogenics (ultra-cold research)

Why Kelvin?

• Absolute scale (no negative values)
• Directly proportional to thermal energy
• Required for gas laws, thermodynamic equations
• International standard for scientific communication

Celsius (°C) is also widely used in:

• Practical laboratory work
• Biology and life sciences
• Environmental science
• Engineering applications

Key distinction: Kelvin for theoretical/fundamental work; Celsius for practical measurements.

Is there a temperature where Celsius and Fahrenheit are equal?

Yes! -40 degrees is where Celsius and Fahrenheit scales intersect: -40°C = -40°F

Why this happens: The formulas create a linear relationship that crosses at one point.

Proof:

• Let °C = °F = x
• Formula: x = (x × 9/5) + 32
• Solving: x = 1.8x + 32
• -0.8x = 32
• x = -40

Practical relevance:

• Extremely cold temperature (colder than most inhabited places)
• Useful reference point for understanding both scales
• Common trivia in science education

Other notable temperatures:

• 0°C = 32°F (water freezes)
• 100°C = 212°F (water boils)
• 37°C = 98.6°F (body temperature)

At what temperature does water boil?

At standard atmospheric pressure (1 atm / 101.325 kPa), water boils at:

• 100°C (Celsius)
• 212°F (Fahrenheit)
• 373.15 K (Kelvin)

Important factors:

• Altitude: Water boils at lower temperatures at high elevations
  • Sea level: 100°C
  • Denver (1,609m): 95°C
  • Mt. Everest summit: 71°C
• Pressure: Higher pressure = higher boiling point
  • Pressure cooker (15 psi): 121°C
  • Atmospheric pressure: 100°C
  • Vacuum: <100°C

Cooking implications:

• High altitude: Longer cooking times needed
• Pressure cooker: Faster cooking due to higher temperature
• Baking adjustments: Recipes need modification at altitude

What is normal human body temperature?

Normal body temperature: 37°C (98.6°F or 310 K)

However, "normal" is actually a range:

• Oral: 36.5-37.5°C (97.7-99.5°F)
• Rectal: 37-38°C (98.6-100.4°F) - most accurate
• Armpit: 36-37°C (96.8-98.6°F) - least accurate
• Ear: 35.8-38°C (96.4-100.4°F)

Variations:

• Time of day: Lower in morning, higher in evening (0.5°C variation)
• Age: Infants and elderly have less stable temperatures
• Activity: Exercise increases temperature
• Menstrual cycle: Slight increase during ovulation

Fever thresholds:

• 38°C/100.4°F: Low-grade fever
• 39°C/102°F: Moderate fever
• 40°C/104°F: High fever
• 41°C/106°F: Dangerous (seek immediate medical care)

Hypothermia:

• <35°C/<95°F: Mild hypothermia
• <32°C/<90°F: Severe hypothermia

Why don't we use the degree symbol (°) with Kelvin?

Reason: Kelvin measures absolute temperature relative to absolute zero, not intervals on an arbitrary scale.

Celsius and Fahrenheit:

• Interval scales based on arbitrary reference points
• "Degrees" denote intervals between these points
• Example: Water freezing/boiling define the scale

Kelvin:

• Absolute scale starting at true zero (no thermal energy)
• Direct measure of thermal energy, not intervals
• No arbitrary reference points

Analogy:

• Distance: We say "5 meters" not "5 degree meters"
• Kelvin is like distance—absolute measurement
• Celsius/Fahrenheit are like coordinates—relative positions

Historical note: Originally called "degrees Kelvin" (°K) until 1967, when the 13th General Conference on Weights and Measures changed it to just "kelvin" (K) to emphasize its absolute nature.

Correct usage:

• ✓ "The temperature is 300 K"
• ✗ "The temperature is 300°K"
• ✓ "An increase of 50 kelvins" or "50 K"
• ✓ "The Kelvin scale"

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Popular Temperature Conversion Pairs

Celsius Conversions:

• Celsius to Fahrenheit →
• Celsius to Kelvin →
• Fahrenheit to Celsius →

Fahrenheit Conversions:

• Fahrenheit to Celsius →
• Fahrenheit to Kelvin →
• Kelvin to Fahrenheit →

Kelvin Conversions:

• Kelvin to Celsius →
• Kelvin to Fahrenheit →
• Celsius to Kelvin →

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