What this converter does
This converter turns energy between calories, kilocalories, joules, kilojoules, BTU, kilowatt-hours, megajoules and foot-pounds — instantly and with exact factors. Type a value, pick the units, and read the answer as you type.
One calorie equals exactly 4.184 joules (the thermochemical calorie); a food “Calorie” is a kilocalorie. For electrical energy over time, see the kWh to kW converter.
The units it covers
Every unit measures energy, so each converts through the joule with a fixed ratio.
View all units & their values
| Unit | Symbol | Value | Mainly used |
|---|---|---|---|
| Calorie | cal | 4.184 | Chemistry, heat (thermochemical) |
| Kilocalorie | kcal | 4184 | Food energy (“Calories”) |
| Joule | J | 1 | SI unit of energy |
| Kilojoule | kJ | 1000 | Food labels, metric energy |
| British thermal unit | BTU | 1055.06 | HVAC, US heating energy |
| Kilowatt-hour | kWh | 3600000 | Electricity billing |
| Megajoule | MJ | 1000000 | Fuels, large energy |
| Foot-pound | ft·lb | 1.35582 | Mechanical work, US units |
The formula
Each unit has a fixed value in joules, so any conversion goes through the joule once:
result = value × factor_from ÷ factor_toWhere:
- value = the number you typed, in the “from” unit
- factor_from = the “from” unit’s value in joules
- factor_to = the “to” unit’s value in joules
Worked example
Convert 500 calories to joules.
1 cal = 4.184 J500 × 4.184 = 2092 JSo 500 calories is 2092 joules, or about 2.09 kilojoules.
The units in this example
The thermochemical calorie, exactly 4.184 joules — the heat to warm one gram of water by about 1 °C. Food “Calories” are kilocalories.
- 1 cal = 4.184 J
- 1 kcal = 1,000 cal
- 1 kcal = 4,184 J
- 1 cal ≈ 0.00397 BTU
The SI unit of energy — one newton-metre of work, or one watt for one second. The base for the other units here.
- 1 J ≈ 0.239 cal
- 1 J = 0.001 kJ
- 1 J ≈ 0.000948 BTU
- 1 J ≈ 0.7376 ft·lb