Convert energy between joules, calories, watt-hours, kilowatt-hours and British thermal units.
Calculations happen locally. We do not send your values to our server.
A watt-hour is exactly 3,600 J, so a kilowatt-hour, the unit on electricity bills, is 3,600,000 J or exactly 3.6 MJ. A 250 kcal snack is 1,046 kJ, and 100,000 BTU is about 29.30710702 kWh.
Every value is normalised to joules with fixed factors and then converted to the unit you choose. A kilocalorie is taken as 4.184 kJ, the thermochemical value, and one BTU as about 1,055.06 J. Different definitions of the BTU and the calorie exist, differing in the fourth or fifth significant digit.
Energy is not the same as power: a 2 kW heater running for 3 hours uses 6 kWh. Air conditioners and heaters are often rated in BTU per hour, which is a power rating, so do not enter it here as if it were an amount of energy. For appliance running costs, use the Electricity Cost Calculator.
Energy converts through the joule. A watt-hour is exactly 3,600 J, so a kilowatt-hour, the unit on electricity bills, is 3,600,000 J or exactly 3.6 MJ. Batteries and power banks are often rated in watt-hours, while gas and heating fuels may be billed in megajoules or kilowatt-hours depending on the country. Energy is not the same as power: a 2 kW heater running for 3 hours uses 6 kWh. For appliance running costs, use the Electricity Cost Calculator.
Food labels in many countries say “Calories” but mean kilocalories. One kilocalorie is 4.184 kJ here, the thermochemical value, so a 250 kcal snack is 1,046 kJ, and a small calorie is one thousandth of that; 1 kJ is about 239.00573614 cal. Labels in the European Union and Australia often show kilojoules first. A 2,000 kcal daily reference intake is about 2.32444444 kWh, a useful way to picture how much energy a body uses compared with household appliances.
The British thermal unit is still used for furnaces, boilers and gas in the United States. One BTU is about 1,055.06 J, and 100,000 BTU, which is one US therm of natural gas, is about 29.30710702 kWh. Air conditioners and heaters are often rated in BTU per hour, which is power rather than energy, so do not enter a BTU/h rating here as if it were an amount of energy. Different definitions of the BTU and calorie exist, differing in the fourth or fifth significant digit.
| Input | Result |
|---|---|
1 kWh → MJ | 3.6 |
1 kcal → kJ | 4.184 |
250 kcal → kJ | 1,046 |
2000 kcal → kWh | 2.32444444 |
100000 BTU → kWh | 29.30710702 |
1 kJ → cal | 239.00573614 |
Food labels in many countries write “Calories” but mean kilocalories. One kilocalorie is 4.184 kJ here, so a 250 kcal snack is 1,046 kJ, while a small calorie is a thousandth of that: 1 kJ is about 239.00573614 cal. Labels in the European Union and Australia often print kilojoules first.
A 2,000 kcal daily reference intake is about 2.32444444 kWh, which is a useful way to picture it next to household electricity. It is roughly what a 2 kW heater would draw in a little over an hour, which shows how much more energy heating and cooking take than the body does.
For furnaces, boilers and natural gas in the United States. One BTU is about 1,055.06 J, and 100,000 BTU, which is one US therm of gas, is about 29.30710702 kWh. Batteries and power banks, by contrast, are rated in watt-hours, and gas or heating bills elsewhere may use megajoules or kilowatt-hours.