Energy Unit Converter: Joules, Calories, kWh, BTU
Convert energy between joules, kilojoules, megajoules, calories, kilocalories, watt-hours, kilowatt-hours and BTU; compare food calories with electricity use.
Things to keep in mind:
- The calorie has more than one definition; some engineering tables use the IT calorie of 4.1868 J, which differs by about 0.07 % (roughly 670 parts per million).
- Converting natural gas from m³ to kWh depends on the gas’s calorific value and is not part of this tool.
- Power (W, kW, horsepower) is not energy but energy per unit of time; use the power unit converter for power units.
Calculator
Result
Enter the values and press Calculate to see the result here.
About this tool
This tool converts an amount of energy between the SI unit joule (J) and its multiples, the calorie and kilocalorie, the watt-hour and kilowatt-hour, and the BTU, and lists the value in every unit.
Formula: result = value × (joules per source unit) ÷ (joules per target unit)
The factors are definitions (NIST SP 811):
- 1 Wh = 3,600 J; 1 kWh = 3,600,000 J = 3.6 MJ
- 1 cal (thermochemical) = 4.184 J; 1 kcal = 4,184 J = 4.184 kJ
- 1 BTU (International Table) = 1,055.05585262 J
The "calorie" on food labels is actually a kilocalorie (kcal); this tool takes 1 kcal = 4.184 kJ.
Example: 1 kWh = 3,600,000 J ÷ 1,000,000 = 3.6 MJ ≈ 860.4207 kcal ≈ 3,412.1416 BTU. A daily diet of 2,000 kcal equals 2,000 × 4,184 ÷ 3,600,000 ≈ 2.32444444 kWh. 500 kcal is 2,092 kJ ≈ 0.581111 kWh ≈ 1,982.833416 BTU; 12,000 BTU ≈ 3.51685284 kWh.
How to read the result The "Result" field is the value in your target unit (8 decimals); the list shows the same energy in every unit with 6 decimals. The conversion factor tells how many target units one source unit equals. Mind the calorie definition: this tool uses the thermochemical calorie (1 cal = 4.184 J).
Electricity bills use kWh, gas bills kWh and m³, and air conditioners and boilers are rated in BTU or kcal. For power (energy per unit of time: W, kW, horsepower) use the power unit converter.
How to use
- Enter the amount of energy you want to convert.
- Select its unit under From unit.
- Select the unit you want the result in under To unit.
- Select Calculate; equivalents in all units are listed as well.
Notes
The main result is rounded half-up (HALF_UP) to 8 decimals, the unit equivalents to 6 and the conversion factor to 10 decimals. The calorie is the thermochemical calorie (4.184 J); the International Table calorie (4.1868 J) is not used.
Frequently asked questions
1 kWh = 3,600,000 J ÷ 4,184 ≈ 860.42 kcal (≈ 860,421 cal).
Yes; the food "Calorie" is a kilocalorie (kcal). 1 kcal = 4.184 kJ, and labels show both.
The International Table BTU is 1,055.05585262 J. 1 kWh ≈ 3,412.14 BTU.
kW is power (rate of use), kWh is energy (total use). A 2 kW appliance running for 3 hours uses 6 kWh.
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