How to use the energy converter
- 1 Type the value you want to convert.
- 2 Choose the unit to convert from and the unit to convert to.
- 3 Press ⇄ to swap the two units.
- 4 Read the result, and see the same energy in every other unit in the table below.
Energy on bills and labels
Electricity is billed in kWh, gas in units, MJ or BTU depending on the country, and food energy in kcal or kJ. Converting them to one unit makes costs easy to compare. Power ratings in kW or hp are a different quantity; use the Power Converter for those.
- Energy = power × time: a 2 kW heater for 3 hours uses 6 kWh.
- 1 kcal heats about 1 litre of water by 1 °C.
- Gas meters may record cubic metres, which the supplier converts to energy using the gas's heat value.
Features
Ten energy units
From electronvolts to megajoules.
Food and bills
kcal and kJ for food labels, kWh for electricity, BTU for heating and cooling.
Exact factors
1 kWh = 3.6 MJ and 1 kcal = 4.184 kJ.
When to use it
Food labels
Labels show both kJ and kcal. 2,000 kcal is 8,368 kJ. For body measures, see the BMI Calculator.
Electricity and gas bills
Compare electricity in kWh with gas billed in MJ or BTU. 1 kWh is 3,412 BTU. For power ratings, use the Power Converter.
Air conditioners
Cooling capacity in BTU per hour is power, not energy; a 12,000 BTU/h unit is 1 ton.
Science homework
Convert between joules, electronvolts and calories for physics and chemistry.
Related Unit tasks
Frequently asked questions
How many joules in a kWh?
3,600,000 joules, or 3.6 megajoules.
How do I convert kcal to kJ?
Multiply by 4.184. A 250 kcal snack is 1,046 kJ.
Is a food Calorie the same as a kcal?
Yes. A food Calorie with a capital C is a kilocalorie, 1,000 small calories.
How many BTU in a kWh?
3,412.14 BTU.
What is the difference between energy and power?
Energy is an amount, such as kWh; power is the rate of using it, such as kW. A 1 kW heater uses 1 kWh of energy in one hour.
What is a megajoule?
One million joules, about 0.278 kWh. Gas bills in some countries use MJ.
What is an electronvolt?
The energy an electron gains across one volt, 1.602 × 10⁻¹⁹ joules. It is used in atomic and particle physics.
How many calories does it take to boil water?
Heating 1 litre of water by 1 °C takes about 1 kcal, so heating it from 20 °C to 100 °C takes about 80 kcal, or 335 kJ, before losses.
Which calorie is used here?
The thermochemical calorie of exactly 4.184 joules, used for food energy.
Which BTU is used?
The International Table BTU of 1,055.06 joules, the usual value for heating and cooling.
How do I read the energy on a food label?
Labels list energy per serving and per hundred grams, usually in both kilojoules and kilocalories. Compare the same basis, and remember a kilocalorie is the Calorie used in diet advice.
Is a kilowatt-hour a lot of energy?
It is enough to run a one kilowatt heater for an hour, a fridge for about a day, or an LED bulb for several days, depending on its rating.
How can I cut my energy use at home?
Heating, cooling and water heating use the most energy in most homes. Better insulation, efficient inverter appliances and turning things off when not in use make the biggest difference over a year.
Why do some countries bill gas in units of energy?
Gas quality varies, so the same volume can carry slightly different energy. Billing in kilowatt-hours or megajoules makes the charge match the energy you actually received.
Built and reviewed by Hamza Farooq, founder and lead developer
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