Energy Converter
Food calories, kilojoules, watt-hours, kilowatt-hours and BTUs.
Energy Converter
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Units in this category
| Unit | Symbol | Exactly |
|---|---|---|
| joules (J) | J | 0.001 kJ |
| kilojoules (kJ) | kJ | reference unit for this category |
| calories (cal) | cal | 0.004184 kJ |
| kilocalories (food calories) (kcal) | kcal | 4.184 kJ |
| watt-hours (Wh) | Wh | 3.6 kJ |
| kilowatt-hours (kWh) | kWh | 3,600 kJ |
| BTUs (Btu) | Btu | 1.055056 kJ |
Where these factors come from
The food Calorie is exactly one kilocalorie = 4.184 kJ (thermochemical definition); a kilowatt-hour is exactly 3.6 MJ. Energy conversions are therefore exact, including food-label comparisons.
All 42 energy pairs
| from → to | J | kJ | cal | kcal | Wh | kWh | Btu |
|---|---|---|---|---|---|---|---|
| J (joule) | — | 0.001 | 0.23900574 | 0.0002390057 | 0.0002777778 | 0.0000002778 | 0.0009478171 |
| kJ (kilojoule) | 1,000 | — | 239.006 | 0.23900574 | 0.27777778 | 0.0002777778 | 0.94781712 |
| cal (calorie) | 4.184 | 0.004184 | — | 0.001 | 0.0011622222 | 0.0000011622 | 0.0039656668 |
| kcal (kilocalory) | 4,184 | 4.184 | 1,000 | — | 1.162222 | 0.0011622222 | 3.965667 |
| Wh (watt-hour) | 3,600 | 3.6 | 860.421 | 0.86042065 | — | 0.001 | 3.412142 |
| kWh (kilowatt-hour) | 3,600,000 | 3,600 | 860,420.65 | 860.421 | 1,000 | — | 3,412.14 |
| Btu (BTU) | 1,055.06 | 1.055056 | 252.164 | 0.2521644 | 0.29307107 | 0.0002930711 | — |
Conversions by starting unit
joules (J)
J to kJJ to calJ to kcalJ to WhJ to kWhJ to Btu
kilojoules (kJ)
kJ to JkJ to calkJ to kcalkJ to WhkJ to kWhkJ to Btu
calories (cal)
cal to Jcal to kJcal to kcalcal to Whcal to kWhcal to Btu
kilocalories (food calories) (kcal)
kcal to Jkcal to kJkcal to calkcal to Whkcal to kWhkcal to Btu
watt-hours (Wh)
Wh to JWh to kJWh to calWh to kcalWh to kWhWh to Btu
kilowatt-hours (kWh)
kWh to JkWh to kJkWh to calkWh to kcalkWh to WhkWh to Btu
BTUs (Btu)
Btu to JBtu to kJBtu to calBtu to kcalBtu to WhBtu to kWh
Common questions
Why do food labels say kcal but people say calories?
The food Calorie (capital C) is one kilocalorie — 1000 small calories, or 4.184 kJ. US labels use Calories; Australian and EU labels often show kJ alongside.
How many kWh is a full battery charge?
A typical EV battery is 50–80 kWh. One kWh is 3.6 megajoules — the kWh↔kJ and kWh↔MJ pages show the arithmetic.
Is a Btu a lot of energy?
One Btu is about 1.055 kJ — the heat from burning one match is roughly 1 Btu. Air conditioners are rated in thousands of Btu per hour.