Energy Converter
Convert kilojoules and calories on food labels, kilowatt-hours and megajoules on energy bills, BTUs and therms — all through the joule. Results update as you type; exact factors shown.
One kilojoule is 0.239 kilocalorie (food Calorie) — see the exact factor, not a rounded rule of thumb.
How the energy converter works
Energy converts through the joule. A thermochemical calorie is exactly 4.184 J, so a food Calorie (kcal) is 4.184 kJ. A kilowatt-hour is exactly 3.6 MJ. A BTU is 1,055.056 J and a US therm is 100,000 BTU.
The UK is metric for most trade and science but keeps miles, pints, stone and mpg (with the imperial gallon) in daily life.
Common energy conversions
| From | To | Units |
|---|---|---|
| 1 kcal | 4.184 kJ | kilocalorie (food Calorie) to kilojoules |
| 1 kJ | 0.239 kcal | kilojoule to kilocalorie (food Calorie) |
| 1 kWh | 3.6 MJ | kilowatt-hour to megajoules |
| 1 kWh | 3,412.1416 BTU | kilowatt-hour to British thermal units |
| 2,000 kcal | 8,368 kJ | kilocalorie (food Calorie) to kilojoules |
| 8,700 kJ | 2,079.3499 kcal | kilojoules to kilocalorie (food Calorie) |
| 1 thm | 29.3071 kWh | therm (US) to kilowatt-hours |
| 1 MJ | 0.2778 kWh | megajoule to kilowatt-hours |
| 100 BTU | 105.5056 kJ | British thermal units to kilojoules |
| 1 ft·lb | 1.3558 J | foot-pound to joules |
Units in this converter and their exact factors
| Unit | Symbol | One unit in joules |
|---|---|---|
| joule | J | 1 joule |
| kilojoule | kJ | 1,000 joule |
| megajoule | MJ | 1,000,000 joule |
| calorie (thermochemical) | cal | 4.184 joule |
| kilocalorie (food Calorie) | kcal | 4,184 joule |
| watt-hour | Wh | 3,600 joule |
| kilowatt-hour | kWh | 3,600,000 joule |
| British thermal unit | BTU | 1,055.05585262 joule |
| therm (US) | thm | 105,505,585.262 joule |
| foot-pound | ft·lb | 1.3558179483 joule |
FAQFrequently asked questions about energy conversion
How many kilojoules are in a calorie?
A food Calorie (kcal) is 4.184 kJ; a small thermochemical calorie is 4.184 J. Australian labels show kJ, US labels show Calories, UK labels show both.
How many kilojoules should an adult eat per day?
Reference intakes are about 8,700 kJ (2,080 kcal) in Australia, 8,400 kJ (2,000 kcal) in the UK and 2,000 Calories in the US — actual needs vary.
How many megajoules are in a kilowatt-hour?
Exactly 3.6 MJ. Gas bills in Australia are metered in MJ; electricity in kWh.
What is a therm?
100,000 BTU, about 29.3 kWh — the unit on many US gas bills.
How many BTUs are in a kWh?
About 3,412 BTU.
Where these figures come from
- BIPM — The International System of Units (SI Brochure, 9th edition) — definitions of the base and derived units.
- NIST Special Publication 811 — Guide for the Use of the International System of Units — the exact conversion factors used here.
- National Physical Laboratory (NPL) — United Kingdom's national measurement authority.
Last checked: September 2026. Conversion factors are fixed by definition and do not change with tax years or regulations.