Energy Converter
Convert energy units for food, electricity, heating and science, including kcal, kJ, kWh, joules and BTU.
All units
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Energy is measured in different units depending on who is talking. Nutritionists count calories, physicists use joules, utilities bill in kilowatt-hours, and heating engineers rate furnaces in BTU. All of them describe the same physical quantity, so you can convert between them exactly. This converter does that and shows all seven units at once.
How to use the energy converter
- Enter an amount of energy in Value.
- Choose the unit you have and the unit you want.
- Read the result and the full table of units below.
Energy conversion factors
| Unit | In joules |
|---|---|
| 1 joule (J) | 1 |
| 1 kilojoule (kJ) | 1,000 |
| 1 calorie (cal) | 4.184 |
| 1 kilocalorie (kcal, food Calorie) | 4,184 |
| 1 watt-hour (Wh) | 3,600 |
| 1 kilowatt-hour (kWh) | 3,600,000 |
| 1 BTU | 1,055.06 |
Everyday examples
- A 2,000 kcal daily diet is about 8,368 kJ, or about 2.3 kWh. That is roughly the energy a 100-watt bulb uses in a day.
- A 3 kW electric heater running for 2 hours uses 6 kWh, about 20,470 BTU.
- A 12,000 BTU air conditioner (often called “1 ton”) moves about 3.5 kWh of heat per hour.
- A smartphone battery of 15 Wh stores about 54,000 J, or about 12.9 kcal.
Energy vs. power
Energy is an amount, measured in joules or kWh. Power is the rate energy is used, measured in watts. A 1,000 W microwave running for one hour uses 1 kWh of energy. Mixing the two up is the most common mistake when reading electricity bills or appliance labels, so check whether a figure is in W or Wh before you convert.
Frequently asked questions
Is a food Calorie the same as a calorie?
No. The "Calorie" on a food label, sometimes written with a capital C, is a kilocalorie, which is 1,000 small calories. A 250-Calorie snack contains 250 kcal, or about 1,046 kJ.
How do I convert kJ to kcal?
Divide kilojoules by 4.184. Many food labels in Australia, the EU and elsewhere show both. For example, 2,000 kJ is about 478 kcal.
How many BTU are in a kilowatt-hour?
One kilowatt-hour is about 3,412 BTU. That figure is useful for comparing electric heating with gas furnaces or air conditioners rated in BTU.