Energy Converter
Convert between joules, calories, kilowatt-hours, BTU, and foot-pounds.
How energy conversion works
Every energy unit here converts through the joule — the SI base unit of energy. The units on food labels (Calories, capitalized) are actually kilocalories, a source of frequent confusion: one food 'Calorie' equals 1,000 small calories, and both are defined as the energy needed to raise a specific amount of water by 1°C.
Common conversions
- 1 food Calorie (kcal) ≈ 4,184 joules ≈ 4.184 kJ
- 1 kilowatt-hour = 3,600,000 joules — the unit your electricity bill is measured in
- 1 BTU ≈ 1,055 joules ≈ 0.252 kcal
- A typical adult diet is often around 2,000 kcal/day ≈ 8,368 kJ/day
Factors in use
Joules are the base. The tool uses 4.184 J per small calorie, 4,184 J per kilocalorie, 3,600 J per watt-hour, 3,600,000 J per kilowatt-hour, 1,055.05585262 J per BTU and 1.3558179483314003 J per foot-pound. Results update as you type, show up to six decimals and follow your browser's digit grouping. The default converts 1 kcal to kJ.
Worked examples
- 1 kcal = 4.184 kJ, and 2,000 kcal = 8,368 kJ = 2.324444 kWh.
- 250 kcal = 1,046,000 J.
- 1 kWh = 3,412.141633 BTU = 860.42065 kcal.
- 500 Wh = 1,800,000 J, and 60 Wh = 216 kJ.
- 100 cal = 418.4 J, and 1 cal = 0.001 kcal.
- 1,000 BTU = 0.293071 kWh.
Rounding and limits
Joules are tiny, so converting a small amount into kilowatt-hours loses it: 1 J shows as 0 kWh, because the true value is about 0.00000028 and the display stops at six decimals. Convert to Wh or kJ first for small energy amounts. The tool offers no power units; watts and BTU per hour are in the Power Converter, and nothing here works out how long a given power takes to deliver an energy amount.
Smaller and larger conversions
1,200 small calories (cal) is 5.0208 kJ, because one cal is 4.184 J. A household using 5 kWh in a day has used 4,302.10325 food Calories (kcal) of energy, 40 foot-pounds is 54.232718 J, and 2 BTU is 0.586142 Wh.
Foot-pounds here are a unit of energy. The torque converter's lbf·ft has the same dimension but measures twisting force, and the two should not be swapped.
Frequently asked questions
Why does 'Calorie' on food labels mean kilocalorie?
It's a long-standing labeling convention: the capital-C 'Calorie' used in nutrition is always a kilocalorie (1,000 small calories), while the lowercase 'calorie' used in chemistry and physics is the smaller unit. Both units appear in casual use, which is why they get confused.
Why is my electricity bill in kilowatt-hours instead of joules?
A kilowatt-hour is a far more practically sized unit for household energy use — a single joule is a tiny amount of energy (about what it takes to lift an apple one meter), so measuring a month of electricity use in joules would mean dealing with numbers in the billions.
How many kilojoules is a 2,000 kcal day?
Choose kilocalories as the source and kilojoules as the target. 2,000 kcal is 8,368 kJ.
Are cal and kcal the same?
No. A kcal is 1,000 cal. The tool lists them separately, and 1 cal converts to 0.001 kcal.
How many watt-hours are in a joule?
One watt-hour is 3,600 joules. In the tool, 500 Wh becomes 1,800,000 J, so a single joule is only about 0.00028 Wh.