Kilowatt-hour to Joule Converter
Convert kilowatt-hours to joules with our free online energy converter.
Quick Answer
1 Kilowatt-hour = 3600000 joules
Formula: Kilowatt-hour × conversion factor = Joule
Use the calculator below for instant, accurate conversions.
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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.
Kilowatt-hour to Joule Calculator
How to Use the Kilowatt-hour to Joule Calculator:
- Enter the value you want to convert in the 'From' field (Kilowatt-hour).
- The converted value in Joule will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Energy category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Kilowatt-hour to Joule: Step-by-Step Guide
Converting Kilowatt-hour to Joule involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
J = kWh × 3600000Example Calculation:
1 kWh = 3600000 J
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.
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and Standards
The kilowatt-hour is defined as the energy equivalent of one kilowatt (1,000 watts) of power sustained for one hour:
1 kWh = 1,000 W × 1 hour = 3,600,000 joules = 3.6 megajoules
Precise Equivalents
- 1 kWh = 3,600,000 J (exactly)
- 1 kWh = 3.6 MJ (exactly)
- 1 kWh = 1.341 horsepower-hours (mechanical)
- 1 kWh = 859.845 kilocalories (thermochemical)
- 1 kWh = 3,412.14 British thermal units (BTU)
- 1 kWh = 2.655 × 10²² electronvolts
The kilowatt-hour is not an SI unit (the SI unit of energy is the joule), but it is explicitly accepted for use alongside SI units by the International Bureau of Weights and Measures (BIPM) due to its universal adoption in electrical energy metering and commerce.
Power vs. Energy: The Critical Distinction
Kilowatt (kW) measures power—the rate at which energy is being used or generated at a specific moment (analogous to speed on a speedometer).
Kilowatt-hour (kWh) measures energy—the total amount of energy used or generated over time (analogous to distance traveled on an odometer).
Relationship: Energy (kWh) = Power (kW) × Time (hours)
Example: A 2 kW space heater running for 3 hours consumes 2 kW × 3 h = 6 kWh of energy.
and Standards
SI Definition
The joule is the SI derived unit of energy, work, and heat, defined as:
1 joule = the energy transferred when a force of 1 newton acts through a distance of 1 meter
Mathematically:
- 1 J = 1 N·m (newton-meter)
- 1 J = 1 kg·m²/s² (SI base units)
- 1 J = 1 W·s (watt-second)
- 1 J = 1 Pa·m³ (pascal-cubic meter)
Multiple Equivalent Definitions
Mechanical work: 1 J = work done moving an object 1 meter against 1 newton force
Electrical energy: 1 J = energy dissipated passing 1 ampere through 1 ohm resistance for 1 second (1 J = 1 A² · Ω · s = 1 V · A · s)
Kinetic energy: 1 J = kinetic energy of a 2 kg mass moving at 1 m/s (KE = ½mv² = ½ × 2 × 1² = 1 J)
Gravitational potential energy: 1 J = energy to lift ~102 grams by 1 meter on Earth (PE = mgh = 0.102 kg × 9.8 m/s² × 1 m ≈ 1 J)
Thermal energy: 1 J ≈ 0.239 calories (energy to raise 0.239 grams of water by 1°C)
2019 SI Redefinition
The 2019 SI revision redefined the joule based on exact fundamental constants:
- Planck constant (h): Exactly 6.62607015 × 10⁻³⁴ J·s
- Speed of light (c): Exactly 299,792,458 m/s
- Caesium hyperfine frequency: Exactly 9,192,631,770 Hz
Since the joule is defined in terms of kilogram, meter, and second, and these are now defined via fundamental constants, the joule has absolute stability independent of physical artifacts.
Standard Multiples
Kilojoule (kJ): 1 kJ = 1,000 J
- Typical for food energy (1 food Calorie = 4.184 kJ)
- Small appliance energy consumption
Megajoule (MJ): 1 MJ = 1,000,000 J = 1,000 kJ
- Vehicle fuel energy (1 liter gasoline ≈ 32 MJ)
- Industrial processes, home daily energy use
Gigajoule (GJ): 1 GJ = 1,000,000,000 J = 1,000 MJ
- Large-scale energy systems
- Natural gas (1 cubic meter ≈ 38 MJ, 1 therm = 105.5 MJ)
Terajoule (TJ): 1 TJ = 10¹² J
- Power plant output (per day/month)
- National energy statistics
Note: The Kilowatt-hour is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Joule belongs to the imperial/US customary system.
History of the Kilowatt-hour and Joule
and Evolution
The Birth of Electrical Metering (1880s-1890s)
The kilowatt-hour emerged from the practical needs of early electrical utilities. When Thomas Edison opened the Pearl Street Station in Manhattan in September 1882—the world's first commercial central power plant—he needed a way to bill customers for electricity consumption. Early meters measured current flow, but this didn't account for voltage or time, making fair billing difficult.
The breakthrough came with the development of the induction watt-hour meter by Oliver B. Shallenberger in 1888, working for Westinghouse. This electromechanical device used electromagnetic induction to rotate a disc at a speed proportional to power consumption, with the total rotations indicating energy consumed—directly measuring kilowatt-hours. This meter design, refined but fundamentally unchanged, remained the global standard for over a century until the recent transition to digital smart meters.
Standardization and the International Electrical Congress (1893)
The International Electrical Congress held during the 1893 World's Columbian Exposition in Chicago formally adopted standardized electrical units. While the joule was recognized as the scientific unit of energy, the kilowatt-hour was established as the practical unit for electrical power distribution and billing. This dual system—joules in science, kilowatt-hours in commerce—continues today.
Samuel Insull and Modern Utility Economics (1890s-1920s)
Samuel Insull, president of Chicago Edison Company (later Commonwealth Edison), revolutionized the electricity industry in the 1890s by implementing sophisticated pricing structures based on kilowatt-hour consumption. Insull pioneered:
- Load factor optimization: Encouraging off-peak usage through lower kWh rates
- Declining block rates: Lower per-kWh prices for higher consumption, incentivizing electrification
- Demand charges: Separate charges for peak power demand (kW) versus energy consumption (kWh) for industrial customers
Insull's innovations made electricity affordable for middle-class households, transforming it from a luxury to a necessity and accelerating the electrification of America and the world.
The Electrification Revolution (1920s-1960s)
By the 1920s, the kilowatt-hour had become universal for electricity billing in industrialized nations. Rural electrification programs—such as the U.S. Rural Electrification Administration (1935)—brought kilowatt-hour metering to millions of farms and small towns. Post-World War II economic growth drove massive increases in electrical consumption, measured everywhere in kilowatt-hours.
Modern Era: Smart Meters and Real-Time kWh (2000s-Present)
The 21st century brought smart meters that measure kilowatt-hour consumption digitally, often in 15-minute or hourly intervals. These enable:
- Time-of-use (TOU) pricing: Different per-kWh rates based on time of day
- Real-time monitoring: Customers can track kWh usage in real time via apps
- Demand response: Automated load reduction during peak demand
- Net metering: Bidirectional kWh measurement for solar panel owners
Today, kilowatt-hours are also the standard unit for electric vehicle battery capacity, solar panel production, energy efficiency ratings, and carbon footprint calculations tied to electricity consumption.
and Evolution
The Mechanical Equivalent of Heat (1840s-1850s)
James Prescott Joule (1818-1889), an English brewer and amateur scientist, conducted groundbreaking experiments demonstrating that mechanical work and heat are equivalent.
Famous paddle-wheel experiment (1843-1850): Joule built apparatus where falling weights drove paddles that stirred water in an insulated container. He precisely measured:
- Mechanical work input (weight × distance fallen)
- Temperature rise of water
- Established ratio: ~772 foot-pounds of work = 1 BTU of heat
- Modern equivalent: 4.184 joules = 1 calorie
Joule's work was initially met with skepticism but eventually revolutionized thermodynamics by unifying heat and mechanical energy under the first law of thermodynamics (conservation of energy).
Lord Kelvin (William Thomson) and Rudolf Clausius incorporated Joule's findings into the foundation of thermodynamics in the 1850s-1860s.
Adoption as a Unit (1882)
The British Association for the Advancement of Science formally adopted "joule" as the unit of work at its 1882 meeting, honoring James Prescott Joule's contributions. The joule was defined as 10⁷ ergs (the CGS energy unit).
Early definition: 1 joule = 10⁷ erg = 10⁷ g·cm²/s²
This established the joule in the meter-kilogram-second (MKS) system, precursor to SI.
International System of Units (1960)
The 11th General Conference on Weights and Measures (CGPM) in 1960 established the International System of Units (SI), designating the joule as the official SI unit for energy, work, and heat.
Unified energy unit: The joule replaced multiple historical units:
- Calorie (thermochemistry, nutrition)
- Erg (CGS physics)
- Foot-pound (engineering)
- Watt-hour (electricity)
- BTU (heating/cooling)
Despite SI adoption, many of these units persist in specific contexts (food Calories, kWh for electricity billing, BTU for HVAC).
Modern Precision (1990s-2019)
1990 redefinition: Linked to the volt and ohm through quantum electrical standards (Josephson effect and quantum Hall effect), enabling unprecedented precision.
2019 SI revision: Redefined the joule via exact fundamental constants (Planck constant, speed of light), eliminating dependence on physical prototypes. This "New SI" provides ultimate stability—joule can be reproduced anywhere in the universe using only constants and measurement equipment.
Common Uses and Applications: kilowatt-hours vs joules
Explore the typical applications for both Kilowatt-hour (imperial/US) and Joule (imperial/US) to understand their common contexts.
Common Uses for kilowatt-hours
1. Electricity Billing (Residential, Commercial, Industrial)
The kilowatt-hour is the universal unit for billing electrical energy consumption worldwide. Your electric utility meter tracks cumulative kilowatt-hours, and your monthly bill reflects the total kWh consumed multiplied by your rate structure.
Typical billing components:
- Energy charge: $0.08-0.35 per kWh (varies by location and utility)
- Delivery/distribution charge: Often a separate per-kWh fee
- Fixed charges: Monthly connection fees independent of kWh
- Demand charges (commercial/industrial): Based on peak kW demand
Example bill calculation (900 kWh residential):
- Energy: 900 kWh × $0.12 = $108.00
- Delivery: 900 kWh × $0.04 = $36.00
- Fixed charge: $10.00
- Total: $154.00
2. Appliance Energy Efficiency Ratings
EnergyGuide labels in the US and Canada display estimated annual kilowatt-hour consumption:
- Refrigerators: 300-700 kWh/year
- Dishwashers: 200-400 kWh/year
- Washing machines: 150-500 kWh/year
Energy Star certification requires appliances to use fewer kWh than standard models, typically 10-50% more efficient.
3. Electric Vehicle Specifications
EV manufacturers specify battery capacity in kilowatt-hours, directly comparable across all brands:
- Small battery: 40-50 kWh (city cars, ~150-200 miles)
- Medium battery: 60-75 kWh (mainstream EVs, ~250-300 miles)
- Large battery: 85-100 kWh (luxury/performance EVs, ~350-400 miles)
- Truck/SUV battery: 100-200+ kWh (heavy vehicles, towing capability)
Efficiency metric: Miles per kWh (analogous to miles per gallon for gasoline vehicles)
4. Solar and Renewable Energy Production
Solar installers and monitoring systems display production in kilowatt-hours:
- Real-time production: "Currently generating 4.2 kW"
- Daily total: "Produced 28 kWh today"
- Lifetime total: "System has produced 47,500 kWh since installation"
Net metering: Bidirectional meters track both kWh consumed from the grid and kWh exported to the grid, with the difference billed (or credited) monthly.
5. Carbon Footprint Calculations
Carbon emissions from electricity are calculated using kilowatt-hour consumption multiplied by regional grid intensity:
Grid carbon intensity (kg CO₂ per kWh):
- Coal-heavy grid: 0.8-1.0 kg CO₂/kWh (e.g., Wyoming, West Virginia)
- US average: ~0.4 kg CO₂/kWh
- Natural gas grid: 0.4-0.5 kg CO₂/kWh
- Renewable-heavy grid: 0.02-0.1 kg CO₂/kWh (e.g., Iceland, Norway, Quebec)
Example: 900 kWh monthly consumption × 0.4 kg CO₂/kWh = 360 kg CO₂ = 0.36 metric tons CO₂ per month
6. Battery Storage Systems (Home and Grid)
Home battery storage (e.g., Tesla Powerwall) and grid-scale battery systems specify capacity in kilowatt-hours:
- Tesla Powerwall 2: 13.5 kWh usable capacity
- LG Chem RESU: 9.8-16 kWh
- Sonnen eco: 5-15 kWh (modular)
Backup capability: A 13.5 kWh battery can power essential loads (refrigerator, lights, WiFi, phone charging) for 1-2 days during an outage.
When to Use joules
Physics and Science
The joule is the universal energy unit in scientific research:
Mechanics: Kinetic energy (KE = ½mv²), potential energy (PE = mgh), work (W = F·d)
Thermodynamics: Heat transfer, enthalpy, internal energy, entropy (S units: J/K)
Electromagnetism: Electrical energy (E = V·I·t), magnetic energy (E = ½LI²), capacitor energy (E = ½CV²)
Quantum mechanics: Energy levels in atoms/molecules (though electronvolts often preferred)
Relativity: Mass-energy equivalence E = mc² (in joules when using SI units)
Engineering Applications
Engineers use joules across all disciplines:
Mechanical engineering: Impact energy, spring energy (E = ½kx²), rotational energy (E = ½Iω²)
Civil engineering: Structural load energy, seismic energy absorption
Aerospace engineering: Rocket propulsion energy, orbital energy calculations
Chemical engineering: Heat of reaction, activation energy, process energy requirements
Materials science: Fracture energy, strain energy density
Electrical and Electronics
Joules quantify electrical energy consumption:
Power consumption: Energy (J) = Power (W) × Time (s)
- 100W light bulb for 1 hour = 100 × 3,600 = 360,000 J = 360 kJ
Battery capacity: Often listed in watt-hours (Wh), convert to joules by × 3,600
- 10 Wh battery = 10 × 3,600 = 36,000 J = 36 kJ
Capacitor energy: E = ½CV² (where C in farads, V in volts, E in joules)
Energy efficiency: Comparing joules input vs. joules output determines efficiency percentage
Nutrition and Food Science
Many countries mandate both kilojoules and Calories on nutrition labels:
Australia/New Zealand: Kilojoules (kJ) primary, Calories secondary
European Union: Often lists both kJ and kcal
Conversion: 1 food Calorie (kcal) = 4.184 kJ
Example: 500 kJ = 500 ÷ 4.184 ≈ 120 kcal (Calories)
Climate and Energy Policy
Joules (typically in TJ, PJ, EJ) measure large-scale energy:
National energy consumption: Reported in exajoules (EJ = 10¹⁸ J) annually
- World primary energy: ~600 EJ/year
- United States: ~100 EJ/year
Carbon footprint: kg CO₂ per GJ of energy source
Renewable energy: Solar irradiance (W/m² → J/m² over time)
Energy intensity: Economic output per joule consumed (GDP/GJ)
Sports and Exercise Science
Joules measure human energy expenditure:
Metabolic equivalent (MET): 1 MET = ~4.184 kJ/hour per kg body weight at rest
Cycling power meters: Measure work in kilojoules per ride
Weightlifting: Work = weight × height × 9.8 (in joules)
- Deadlift 100 kg to 1 meter height = 100 × 9.8 × 1 = 980 J
Running economy: Joules per meter traveled
Additional Unit Information
About Kilowatt-hour (kWh)
How much does 1 kWh of electricity cost?
Electricity rates vary widely by location, utility, rate structure, and time of day:
US average (2024): $0.13-0.16 per kWh (residential)
By state (residential, wide variation):
- Lowest: Louisiana (~$0.09/kWh), Oklahoma (~$0.10/kWh), Arkansas (~$0.10/kWh)
- Highest: Hawaii (~$0.40/kWh), California (~$0.25-0.35/kWh), Massachusetts (~$0.24/kWh)
- Typical ranges: Most states $0.10-0.18/kWh
International comparison:
- Denmark: ~$0.40/kWh (highest in developed world)
- Germany: ~$0.35/kWh
- UK: ~$0.25-0.30/kWh (£0.20-0.24/kWh)
- Canada: ~$0.08-0.12/kWh (varies by province)
- China: ~$0.08/kWh (residential)
Commercial rates are typically 20-40% lower than residential ($0.08-0.12/kWh in US), while industrial rates are often 40-60% lower ($0.05-0.08/kWh) due to higher volumes and lower distribution costs.
Time-of-use (TOU) rates vary by time:
- Off-peak (midnight-6am): $0.08-0.12/kWh
- Mid-peak (daytime): $0.12-0.18/kWh
- On-peak (5-9pm): $0.20-0.40/kWh
What is the difference between kW and kWh?
This is one of the most common sources of confusion in electricity:
Kilowatt (kW) measures POWER—the rate of energy use or generation at a specific instant.
- Analogous to: Speed (miles per hour on speedometer)
- Measures: How fast energy is being used right now
- Example: "My air conditioner is currently drawing 3.5 kW"
Kilowatt-hour (kWh) measures ENERGY—the total amount of energy used or generated over time.
- Analogous to: Distance (total miles traveled on odometer)
- Measures: How much energy was used over a period
- Example: "My air conditioner used 28 kWh today (3.5 kW × 8 hours)"
Relationship: Energy (kWh) = Power (kW) × Time (hours)
Another analogy: Think of filling a bathtub:
- kW = flow rate (gallons per minute from faucet)
- kWh = total water (total gallons in tub)
- Fast flow × short time = Slow flow × long time = same total water
Billing distinction: You're billed for energy (kWh), not power (kW)—except for commercial "demand charges" based on peak kW.
How many kWh does an average home use per day?
US average: ~30 kWh per day (~900 kWh per month, ~10,800 kWh per year)
Breakdown by category (typical US home):
- Heating/cooling: 40-45% (~12-14 kWh/day)
- Water heating: 14-18% (~4-5 kWh/day)
- Appliances: 25-30% (~8-9 kWh/day)
- Lighting: 6-10% (~2-3 kWh/day)
- Electronics: 5-8% (~2 kWh/day)
Variation by home type:
- Apartment (500-800 sq ft): 15-20 kWh/day
- Small house (1,000-1,500 sq ft): 20-25 kWh/day
- Medium house (1,500-2,500 sq ft): 25-35 kWh/day
- Large house (2,500-4,000 sq ft): 35-50 kWh/day
- Very large home (4,000+ sq ft): 50-100+ kWh/day
Seasonal variation:
- Winter (heating climate): 30-50 kWh/day
- Spring/Fall: 20-30 kWh/day
- Summer (cooling climate): 35-60 kWh/day
Geographic variation (US average by region):
- South (Louisiana, Texas, Florida): 35-45 kWh/day (high AC usage)
- West (California, Oregon): 20-30 kWh/day (mild climate)
- Northeast (New York, Massachusetts): 25-30 kWh/day
- Midwest (Illinois, Ohio): 28-35 kWh/day
How do I calculate my appliance's kWh usage?
Formula: kWh = (Watts ÷ 1,000) × Hours of use
Step-by-step:
- Find wattage: Check appliance label or manual (or use a Kill-A-Watt meter)
- Convert to kilowatts: Divide watts by 1,000
- Multiply by hours: Total hours of operation
- Result is kWh: Total energy consumed
Example 1 (Simple continuous use):
- 60-watt light bulb
- Used 5 hours per day
- kWh per day = (60 ÷ 1,000) × 5 = 0.06 × 5 = 0.3 kWh
- Monthly = 0.3 × 30 = 9 kWh
- Cost = 9 kWh × $0.15 = $1.35 per month
Example 2 (Cycling appliance):
- Refrigerator with 150-watt compressor
- Runs ~8 hours per day (33% duty cycle)
- kWh per day = (150 ÷ 1,000) × 8 = 0.15 × 8 = 1.2 kWh
- Yearly = 1.2 × 365 = 438 kWh
- Cost = 438 kWh × $0.15 = $65.70 per year
Example 3 (High-power short duration):
- Electric oven, 3,000 watts
- Used 1 hour per day
- kWh per day = (3,000 ÷ 1,000) × 1 = 3 kWh
- Monthly = 3 × 30 = 90 kWh
- Cost = 90 kWh × $0.15 = $13.50 per month
Tip: For cycling appliances (refrigerators, AC, heaters), check EnergyGuide labels for actual annual kWh rather than calculating from power ratings.
How many kWh does it take to charge an electric vehicle?
Charging kWh depends on battery size and state of charge:
Formula: kWh needed = Battery capacity (kWh) × (% to charge ÷ 100) ÷ Charging efficiency
Charging efficiency: ~85-95% (some energy lost to heat)
Example 1 (Typical daily charging):
- Tesla Model 3 Long Range (82 kWh battery)
- Daily driving uses 40% of battery (33 kWh)
- Charging efficiency: 90%
- kWh from wall = 33 ÷ 0.90 = 36.7 kWh
- Cost at $0.15/kWh = $5.50 per charge
Example 2 (Empty to full):
- Nissan Leaf (62 kWh battery)
- Charging from 10% to 100% (90% of capacity)
- kWh needed = 62 × 0.90 = 55.8 kWh
- With 90% efficiency = 55.8 ÷ 0.90 = 62 kWh
- Cost at $0.12/kWh = $7.44 full charge
Charging levels:
- Level 1 (120V, 12A): ~1.4 kW → ~1.4 kWh per hour (very slow)
- Level 2 (240V, 32A): ~7.7 kW → ~7.7 kWh per hour (home charging)
- DC Fast Charging: 50-350 kW → 50-350 kWh per hour (public fast charging)
Annual EV consumption (typical):
- 12,000 miles per year ÷ 4 miles per kWh = 3,000 kWh per year
- Cost at $0.15/kWh = $450 per year
- Gasoline equivalent (25 MPG, $3.50/gal): 480 gallons = $1,680 per year
- Savings: ~$1,200 per year
How many kilowatt-hours are in a gallon of gasoline?
Gasoline contains approximately 33.7 kWh of chemical energy per gallon (based on lower heating value).
However, internal combustion engines are only 20-30% efficient at converting this to mechanical work, while electric motors are 85-95% efficient.
Effective comparison:
- 1 gallon gasoline = 33.7 kWh chemical energy
- Usable mechanical energy = 33.7 × 0.25 (avg efficiency) = 8.4 kWh
- Electric vehicle uses 8.4 kWh directly from battery = equivalent to ~1 gallon gasoline
Example: A 25 MPG gas car vs. 4 miles/kWh EV:
- Gas car: 100 miles ÷ 25 MPG = 4 gallons = 134.8 kWh chemical energy (33.7 usable)
- EV: 100 miles ÷ 4 mi/kWh = 25 kWh from battery
- Efficiency advantage: EV uses ~25% of the energy (25 kWh vs. 100 kWh delivered fuel)
Cost comparison (at $3.50/gal gasoline, $0.15/kWh electricity):
- Gas: 4 gallons × $3.50 = $14.00 per 100 miles
- Electric: 25 kWh × $0.15 = $3.75 per 100 miles
- Savings: $10.25 per 100 miles, or ~73% cheaper
What is a megawatt-hour (MWh) or gigawatt-hour (GWh)?
These are larger units used for industrial, utility, and national-scale energy:
Megawatt-hour (MWh): 1 MWh = 1,000 kWh
- Scale: Enough for ~1.5 months of average US household consumption
- Uses: Large commercial buildings, small industrial facilities, utility contracts
- Example: A small office building might use 50-100 MWh per month
Gigawatt-hour (GWh): 1 GWh = 1,000 MWh = 1,000,000 kWh
- Scale: Enough for ~100 US homes for one year
- Uses: Large industrial plants, small utility service territories, data centers
- Example: A medium-sized data center uses 10-50 GWh per year
Terawatt-hour (TWh): 1 TWh = 1,000 GWh = 1,000,000 MWh = 1,000,000,000 kWh
- Scale: National and global electricity consumption
- Example: California uses ~290 TWh per year; US total ~4,000 TWh per year
Power plant output example:
- 1,000 MW (1 GW) nuclear plant running continuously for 1 year:
- 1,000 MW × 8,760 hours/year = 8,760 GWh = 8.76 TWh
How accurate are electricity meters?
Modern electricity meters are extremely accurate:
Electromechanical meters (older spinning disc meters):
- Accuracy: ±1-2% over most load ranges
- More accurate at higher loads, less accurate at very low loads
- Degrade slowly over time; calibrated to read slightly high initially
Digital smart meters (solid-state):
- Accuracy: ±0.5-1% across all load ranges
- Highly accurate even at very low loads (phantom/standby power)
- Consistent accuracy over time (no mechanical wear)
Regulatory standards (US):
- ANSI C12.20 Class 0.2: ±0.2% accuracy (revenue-grade meters)
- Utilities must test meters periodically; out-of-spec meters must be replaced
Practical impact: A 1% error on a 1,000 kWh monthly bill = 10 kWh = $1-2 difference. Given meters tend to read slightly high, customers rarely underpay.
If you suspect meter error:
- Check for obvious high-consumption causes (always-on appliances, inefficient equipment)
- Turn off all breakers except one circuit; use a known load (e.g., 1,000W heater) and time it
- Request utility meter test (usually free or low-cost; if meter is faulty, utility pays; if accurate, small fee)
Can I run my house on a generator? How many kWh?
Generator sizing: Based on power (kW), not energy (kWh)
Average home needs:
- Essential loads only (fridge, lights, electronics): 2-4 kW
- Partial home (add well pump, sump pump, furnace): 5-7 kW
- Whole home without AC: 8-12 kW
- Whole home with central AC: 15-22 kW
Fuel consumption and kWh:
- Portable generators: ~0.5-0.75 gallons/hour per kW output
- Example: 5 kW generator at 50% load (2.5 kW) uses ~1.5 gal/hr
- Running 8 hours = 12 gallons = 12 × 33.7 kWh = 404 kWh chemical → ~100 kWh electrical @ 25% efficiency
Cost comparison:
- Grid electricity: 100 kWh × $0.15 = $15.00
- Generator: 12 gallons × $3.50/gal = $42.00 (plus maintenance, noise, emissions)
Battery backup alternative: A 13.5 kWh Tesla Powerwall can provide 13.5 kWh of energy (enough for essential loads for 1-2 days during outage), recharged by solar or grid.
How many solar panels do I need to generate X kWh?
Solar panel output: 250-400 watts per panel (newer panels ~350-400W)
Production formula: kWh = Panel wattage (kW) × Peak sun hours × System derate
Peak sun hours (daily average, varies by location and season):
- Southwest US (Arizona, Nevada): 5.5-7 hours
- California: 5-6 hours
- Southern US: 4.5-5.5 hours
- Northern US: 3.5-4.5 hours
System derate factor: ~0.75-0.80 (accounts for inverter efficiency, shading, temperature, wiring losses)
Example 1 (30 kWh per day in Arizona):
- Target: 30 kWh/day
- Location: Phoenix (6 peak sun hours)
- System needed: 30 ÷ (6 × 0.77) = 6.5 kW system
- Number of 350W panels: 6,500 W ÷ 350 W/panel = 19 panels
- Annual production: 30 kWh/day × 365 = 10,950 kWh/year
Example 2 (900 kWh per month in Massachusetts):
- Target: 900 kWh/month = 30 kWh/day
- Location: Boston (4 peak sun hours)
- System needed: 30 ÷ (4 × 0.77) = 9.7 kW system
- Number of 350W panels: 9,700 W ÷ 350 W/panel = 28 panels
Rule of thumb: In average US locations (4.5 peak sun hours), a 1 kW system produces ~1,300-1,500 kWh per year.
About Joule (J)
How do I convert joules to calories?
Formula: calories = joules ÷ 4.184
Examples:
- 4,184 J = 1,000 small calories = 1 kcal (food Calorie)
- 100 J = 100 ÷ 4.184 ≈ 23.9 calories
- 1,000 J = 1,000 ÷ 4.184 ≈ 239 calories
For food Calories (kcal): joules ÷ 4,184 = kcal
- 418,400 J ÷ 4,184 = 100 kcal (food Calories)
How do I convert joules to kWh?
Formula: kWh = joules ÷ 3,600,000
Why 3,600,000?: 1 kWh = 1,000 watts × 3,600 seconds = 3,600,000 joules
Examples:
- 3,600,000 J = 1 kWh
- 1,800,000 J = 0.5 kWh
- 108,000,000 J = 30 kWh (typical home daily use)
How much energy is 1 joule?
Physical examples:
- Lifting 100 grams (small apple) 1 meter against Earth's gravity
- 1 watt of power for 1 second
- Kinetic energy of 2 kg mass moving at 1 m/s
- Energy to heat 0.24 grams of water by 1°C
Perspective: 1 joule is small—about the energy in a single heartbeat. Practical applications typically use kilojoules (kJ), megajoules (MJ), or kilowatt-hours (kWh).
What is the relationship between watts and joules?
Power (watts) = Energy (joules) ÷ Time (seconds)
Or equivalently: Energy (joules) = Power (watts) × Time (seconds)
Definition: 1 watt = 1 joule per second (W = J/s)
Examples:
- 100W light bulb for 10 seconds = 100 × 10 = 1,000 J = 1 kJ
- 1,000W microwave for 2 minutes = 1,000 × 120 = 120,000 J = 120 kJ
- 1W for 1 hour = 1 × 3,600 = 3,600 J = 3.6 kJ
Takeaway: Watts measure the rate of energy use; joules measure the total amount of energy.
Why do energy bills use kWh instead of joules?
Historical reasons: Kilowatt-hours (kWh) became standard for electricity billing before SI joule adoption (1960).
Convenient numbers: Home electricity typically measures 10-50 kWh/day, equivalent to 36-180 MJ/day. Using joules would require large numbers (millions).
Industry inertia: Billions of meters and billing systems use kWh; switching would require enormous infrastructure investment.
Conversion: 1 kWh = 3,600,000 J = 3.6 MJ
Both valid: kWh and MJ are both acceptable SI-compatible units for electrical energy.
How many joules are in a food Calorie?
1 food Calorie (capital C, kilocalorie) = 4,184 joules = 4.184 kilojoules
Important distinction:
- Small calorie (cal): 4.184 J
- Food Calorie (Cal, kcal): 4,184 J = 4.184 kJ
Examples:
- 100 Calorie snack = 418,400 J = 418.4 kJ
- 2,000 Calorie daily intake = 8,368,000 J = 8.368 MJ
- Banana (105 Calories) = 439,320 J ≈ 439 kJ
Labeling variation: Some countries (Australia, EU) show energy in both kJ and kcal.
What's the difference between joules and electronvolts?
Both measure energy but use vastly different scales:
Joule (J): SI unit for macroscopic energy (mechanical, thermal, electrical)
Electronvolt (eV): Atomic-scale energy unit (energy gained by electron crossing 1 volt)
Conversion: 1 eV = 1.602 × 10⁻¹⁹ J (extremely tiny in macroscopic terms)
Usage:
- Joules: Everyday physics, engineering, household energy
- Electronvolts: Atomic physics, chemistry, particle physics, semiconductors
Example: Visible light photon ≈ 2 eV ≈ 3.2 × 10⁻¹⁹ J
How do joules relate to kinetic energy?
Kinetic energy formula: KE = ½mv²
Where:
- m = mass (kg)
- v = velocity (m/s)
- KE = kinetic energy (joules)
Examples:
- 1 kg at 1 m/s: KE = ½ × 1 × 1² = 0.5 J
- 10 kg at 10 m/s: KE = ½ × 10 × 10² = 500 J
- 1,000 kg (small car) at 20 m/s (72 km/h): KE = ½ × 1,000 × 20² = 200,000 J = 200 kJ
- 70 kg person at 3 m/s (jogging): KE = ½ × 70 × 3² = 315 J
Note: Kinetic energy grows with velocity squared, so doubling speed quadruples energy.
Can you create or destroy joules?
No, energy (in joules) is conserved according to the first law of thermodynamics (conservation of energy).
Energy can only transform:
- Mechanical → thermal (friction converts motion to heat)
- Chemical → thermal (combustion releases heat)
- Electrical → mechanical (motors convert electricity to motion)
- Nuclear → thermal → mechanical → electrical (nuclear power plants)
Total joules remain constant in isolated systems, though energy may become less useful (second law: entropy increases).
Mass-energy equivalence: Einstein's E = mc² shows mass can convert to energy and vice versa, but total mass-energy (in joules) is conserved.
How many joules does a human use per day?
Basal metabolism (resting): ~7,000,000-9,000,000 J (7-9 MJ = 1,700-2,200 kcal)
Total daily energy expenditure (including activity):
- Sedentary: ~8,000,000-10,000,000 J (8-10 MJ = 2,000-2,400 kcal)
- Moderate activity: ~10,000,000-12,000,000 J (10-12 MJ = 2,400-3,000 kcal)
- Very active: ~12,000,000-16,000,000 J (12-16 MJ = 3,000-4,000 kcal)
- Elite athlete training: ~16,000,000-33,000,000 J (16-33 MJ = 4,000-8,000 kcal)
Energy sources: Carbohydrates (17 kJ/g), proteins (17 kJ/g), fats (37 kJ/g)
Efficiency: Human body ~20-25% efficient at converting food energy to mechanical work; rest becomes heat.
Conversion Table: Kilowatt-hour to Joule
| Kilowatt-hour (kWh) | Joule (J) |
|---|---|
| 0.5 | 1,800,000 |
| 1 | 3,600,000 |
| 1.5 | 5,400,000 |
| 2 | 7,200,000 |
| 5 | 18,000,000 |
| 10 | 36,000,000 |
| 25 | 90,000,000 |
| 50 | 180,000,000 |
| 100 | 360,000,000 |
| 250 | 900,000,000 |
| 500 | 1,800,000,000 |
| 1,000 | 3,600,000,000 |
People Also Ask
How do I convert Kilowatt-hour to Joule?
To convert Kilowatt-hour to Joule, enter the value in Kilowatt-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 energy converter page to convert between other units in this category.
Learn more →What is the conversion factor from Kilowatt-hour to Joule?
The conversion factor depends on the specific relationship between Kilowatt-hour and Joule. 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 Joule back to Kilowatt-hour?
Yes! You can easily convert Joule back to Kilowatt-hour by using the swap button (⇌) in the calculator above, or by visiting our Joule to Kilowatt-hour converter page. You can also explore other energy conversions on our category page.
Learn more →What are common uses for Kilowatt-hour and Joule?
Kilowatt-hour and Joule are both standard units used in energy measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our energy converter for more conversion options.
For more energy conversion questions, visit our FAQ page or explore our conversion guides.
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Other Energy Units and Conversions
Explore other energy units and their conversion options:
- Kilojoule (kJ) • Kilowatt-hour to Kilojoule
- Megajoule (MJ) • Kilowatt-hour to Megajoule
- Gigajoule (GJ) • Kilowatt-hour to Gigajoule
- Watt-hour (Wh) • Kilowatt-hour to Watt-hour
- Megawatt-hour (MWh) • Kilowatt-hour to Megawatt-hour
- Calorie (cal) • Kilowatt-hour to Calorie
- Kilocalorie (kcal) • Kilowatt-hour to Kilocalorie
- British Thermal Unit (BTU) • Kilowatt-hour to British Thermal Unit
- Therm (therm) • Kilowatt-hour to Therm
- Foot-pound (ft⋅lb) • Kilowatt-hour to Foot-pound
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 — Fundamental physical constants and unit conversions
Bureau International des Poids et Mesures — International System of Units (SI) definitions and standards
International Organization for Standardization — Quantities and units international standards series
Last verified: February 19, 2026