Energy Converter
Convert energy between joules, calories, watt-hours and BTU - handy for food labels, electricity bills and heating figures.
About the Energy Converter
This tool converts a quantity of energy between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, British thermal units (BTU) and electronvolts. These units span food labels, electricity bills, heating systems and physics, all of which describe the same underlying quantity in different ways.
How to use it
- Enter the figure you know into its field, such as a food value in kilocalories.
- Read the equivalent in kilojoules, kWh or BTU.
- Use joules and electronvolts for scientific work, or watt-hours for batteries.
A practical example: the "calories" on a food label are actually kilocalories, and 1 kcal equals about 4.184 kJ, which is why a 500 kcal meal is around 2092 kJ. For electricity, 1 kWh equals 3.6 million joules (3600 kJ), useful when comparing appliance ratings to your bill. The tool uses the thermochemical calorie definition. All conversions happen locally in your browser, so the numbers you enter stay private.
Frequently asked questions
How many joules are in a calorie?
One thermochemical calorie equals 4.184 joules. A food Calorie (with a capital C) is actually a kilocalorie, so it equals 4184 joules.
How many kilojoules are in a kilowatt-hour?
One kilowatt-hour equals 3600 kilojoules, or 3,600,000 joules. That is because a kilowatt sustained for one hour (3600 seconds) delivers that much energy.
Are food label calories the same as calories in physics?
No. The Calorie on nutrition labels is a kilocalorie, equal to 1000 small calories. So a 200 Calorie snack is really 200 kcal or about 837 kJ.
What is a BTU in joules?
One British thermal unit is about 1055 joules. BTU is common for heating and air-conditioning ratings, especially in the United States.