About the Energy Converter
Energy turns up in different units depending on who is measuring it: food labels use kilocalories, electricity bills use kilowatt-hours, physics uses joules and heating equipment often still uses BTU. They all measure the same thing.
This converter handles joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours and BTU in any direction.
How it works
Every unit is defined against the joule, so a conversion is one multiplication: value × factor of the source unit ÷ factor of the target unit.
- Pick the unit you have and the one you want.
- Type the value.
- Swap the units to convert back.
| Unit | In joules |
|---|---|
| 1 kilojoule (kJ) | 1,000 J |
| 1 calorie (cal) | 4.184 J |
| 1 kilocalorie (kcal, the 'calorie' on food labels) | 4,184 J |
| 1 watt-hour (Wh) | 3,600 J |
| 1 kilowatt-hour (kWh) | 3,600,000 J |
| 1 BTU | 1,055 J |
Examples
Worked examples:
- A 2,000 kcal daily diet is 2,000 × 4,184 = 8.37 million joules, or about 2.3 kWh — roughly what a washing machine uses in one hot cycle.
- A 1 kWh electricity unit is 3.6 million joules, or about 860 kcal.
- A 10,000 BTU air conditioner moves about 10.55 million joules of heat an hour, which needs roughly 2.9 kW of cooling power.
Note the two different 'calories': the small calorie (4.184 J) and the kilocalorie used on food labels, which is a thousand times larger. The power converter handles the related question of how fast energy is used.
Energy Converter: frequently asked questions
- What is the difference between a calorie and a kilocalorie?
A kilocalorie is 1,000 calories. Food labels write 'calories' but mean kilocalories, so a 500-calorie meal is really 500 kcal, or about 2.1 million joules.
- How many joules are in a kilowatt-hour?
3,600,000. A kilowatt is 1,000 joules per second, and an hour is 3,600 seconds.
- Is BTU still used?
Yes, mainly for heating and air conditioning capacity in the US and India. One BTU is about 1,055 joules; a 12,000 BTU air conditioner is a '1-ton' unit.