Convert energy between joules, calories, kWh, BTU and more.
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How do you convert between joules, calories, kWh and BTU?
Each unit converts through joules: multiply the value by its factor to joules, then divide by the target unit's factor. For example, 1 kWh equals 3,600,000 joules or about 3,412 BTU. Note that food "Calories" are kilocalories, where one Calorie equals 1000 of these calories.
Understanding your result
Food “Calories” are kilocalories; one Calorie equals 1000 of these calories.
Formula and method
Each unit converts through joules: the value is multiplied by its factor to joules, then divided by the target factor (1 kWh = 3,600,000 J).
Assumptions and limitations
Conversions are exact ratios based on the thermochemical calorie (1 cal = 4.184 J) and standard definitions. Note that the food "Calorie" with a capital C on nutrition labels is actually a kilocalorie (1,000 cal). The tool converts a quantity of energy, not power — for a rate of energy use, use watts or horsepower instead.
Worked example
1 kWh equals 3,600,000 joules or about 3,412 BTU.
Common energy conversions
| Convert | Equals |
|---|---|
| 1 kilowatt-hour | 3,600,000 joules |
| 1 kilowatt-hour | 860.421 kilocalories |
| 1 kilocalorie | 4.184 kilojoules |
| 1 kilocalorie | 4,184 joules |
| 1 BTU | 1,055.06 joules |
| 1 kilowatt-hour | 3,412.14 BTU |
| 1 watt-hour | 3,600 joules |
| 1 calorie | 4.184 joules |
How to use this tool
- Enter a value and choose the from and to units.
- The result updates instantly.
Common mistakes to avoid
- Confusing calorie (cal) with food Calorie (kcal).
About the Energy Converter
Convert an energy value between joules, calories, watt-hours, kilowatt-hours and BTU.
Who should use this tool
Students and engineers converting between joules, calories and kilowatt-hours, people comparing food energy (kilocalories) with physical energy units, and anyone reading appliance consumption in kWh or a heating value in BTU. It covers joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours and BTU.
Benefits
- Bridges scientific (joules), nutritional (kcal) and electrical (kWh) energy units
- Uses the exact thermochemical calorie and standard BTU definitions
- Clears up the food-Calorie-versus-calorie confusion
- Private, instant and available offline
Practical use cases
- Converting food energy on a label from kilocalories to kilojoules
- Turning an appliance's kWh usage into joules for a physics problem
- Comparing a heater's BTU rating with its kilowatt equivalent
- Checking energy answers across scientific and everyday units
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Frequently asked questions
How many joules in a kWh?
Exactly 3,600,000 joules.
How many joules are in a kilowatt-hour?
One kilowatt-hour equals 3,600,000 joules (3.6 megajoules), because it is 1,000 watts sustained for 3,600 seconds. That is why electricity is billed in kWh — a single joule is a very small amount of energy.
Is a food Calorie the same as a calorie?
No. The "Calorie" on nutrition labels (capital C) is a kilocalorie — 1,000 small calories, or 4,184 joules. So a 200-Calorie snack holds about 837 kilojoules of energy.