Energy Converter
Convert between joules, calories, BTU, kWh, and more.
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1 kcal = 4.184 kJ
| Kilocalories (food Cal) (kcal) | Kilojoules (kJ) |
|---|---|
| 1 | 4.184 |
| 2 | 8.368 |
| 5 | 20.92 |
| 10 | 41.84 |
| 15 | 62.76 |
| 20 | 83.68 |
| 25 | 104.6 |
| 50 | 209.2 |
| 75 | 313.8 |
| 100 | 418.4 |
| 150 | 627.6 |
| 200 | 836.8 |
| 250 | 1,046 |
| 500 | 2,092 |
| 1,000 | 4,184 |
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Energy Conversion Reference
| From | To |
|---|---|
| 1 kilowatt-hour (kWh) | 3,600,000 J / 3,412 BTU |
| 1 calorie (cal) | 4.184 joules |
| 1 food Calorie (kcal) | 4,184 J / 1,000 calories |
| 1 BTU | 1,055 joules |
Calories vs Kilocalories
When food packaging says "200 Calories," it actually means 200 kilocalories (kcal) — not the scientific calorie used in chemistry. The food Calorie (with a capital C) equals 1 kcal, which equals 1,000 small calories. This naming convention causes endless confusion.
In scientific contexts, use joules (J) or kilojoules (kJ) for energy to avoid ambiguity. A food Calorie is about 4.184 kJ. Your daily energy intake of 2,000 food Calories is roughly 8,368 kJ.
When to use this
You are comparing your electricity bill (measured in kilowatt-hours) with the energy content of natural gas (measured in BTU or therms). Or you are studying physics and need to convert between joules, calories, and electronvolts for a problem set. Or you are reading a nutrition label that lists energy in kilojoules instead of the Calories you are used to. Energy conversion spans physics, engineering, nutrition, and utility billing.
The most commonly searched energy conversions are kWh to joules, calories to joules, BTU to kWh, and kilojoules to calories. This converter handles all of these plus watt-hours, kilocalories (the "Calories" on food labels), and electronvolts. The joule is the SI base unit of energy, so all other units are defined relative to it.
Good to know
Food "Calories" are actually kilocalories. The "Calorie" on a nutrition label (capital C) is 1 kilocalorie = 1,000 small calories = 4,184 joules. In most countries outside the US, food labels show kilojoules (kJ). A 2,000-Calorie diet is about 8,368 kJ. This is the most practical energy conversion for everyday life.
1 kWh = 3,600,000 joules. A kilowatt-hour is the energy consumed by a 1,000-watt appliance running for one hour. It is the standard billing unit for electricity worldwide. At $0.15 per kWh, running a 100-watt light bulb for 10 hours costs about 15 cents.
BTU is the dominant unit in US heating and cooling. A BTU (British Thermal Unit) is the energy needed to raise one pound of water by one degree Fahrenheit. Furnaces, air conditioners, and water heaters are all rated in BTU/hr. One therm (100,000 BTU) is the standard unit on natural gas bills.
Quick Reference
| From | To | Multiply By |
|---|---|---|
| 1 kilocalorie (food Cal) | Joules | 4,184 |
| 1 kilocalorie | Kilojoules | 4.184 |
| 1 kWh | Joules | 3,600,000 |
| 1 kWh | BTU | 3,412 |
| 1 BTU | Joules | 1,055 |
| 1 therm | kWh | 29.3 |
| 1 joule | Calories (small) | 0.2388 |
| 1 electronvolt | Joules | 1.602 x 10^-19 |