Converters
Energy Converter
Convert joules, calories, watt-hours, BTU, and electronvolts.
Free to use — no sign-up or login.
The calorie in this list is the thermochemical calorie, 4.184 J, so one kilocalorie is 4184 J. One kilowatt-hour is 3,600,000 J and displays as 860.421 kcal.
Watts and horsepower are power, not energy. Use the power converter for those.
A food calorie is a kilocalorie
Nutrition labels say “calorie” for what this page calls a kilocalorie. One small calorie (cal) is 4.184 J. One kcal is 1000 of those.
Watt-hours and BTU
One watt-hour is 3600 J. The BTU in the list is the IT BTU, 1055.05585262 J. An electronvolt is 1.602176634×10⁻¹⁹ J and stays in scientific notation.
Worked example: 1 kWh
From kilowatt-hours to kilocalories, 1 kWh displays as 860.421 kcal. From kilocalories to joules, 1 kcal is 4184 J.
\[ 1\,\mathrm{kWh}=3{,}600{,}000\,\mathrm{J}=860.421\,\mathrm{kcal} \]
Frequently asked questions
How many kilocalories are in a kilowatt-hour?
860.421 kcal, using 1 kcal = 4184 J.
Is a food calorie the small calorie?
No. A food calorie is a kilocalorie, 4184 J.
What is a watt-hour?
3600 joules. A kilowatt-hour is 1000 of those.
Why is an electronvolt scientific?
One electronvolt is far below a joule, so the screen keeps scientific notation.
Does this page convert horsepower?
No. Horsepower is power. Use the power converter.
References
Assumptions and limitations
Thermochemical calorie, not a food-database rounding. Six significant digits, with scientific notation for very small energies.