Energy Converter
Convert between joules, calories, kilowatt-hours, BTU, therms and more. Useful for nutrition, physics homework and reading utility bills in whatever unit they arrive in.
Energy and power are easy to confuse — the Power Converter covers rate rather than total, and Pressure rounds out the set.
How to use the Energy Converter
- 1 Enter the energy value you want to convert.
- 2 Select the source unit — joule, kilojoule, calorie, kilocalorie, watt-hour, kilowatt-hour, BTU or electronvolt.
- 3 Read the value in the other units, which makes it easy to compare a food label with an electricity bill.
- 4 Swap direction to convert the other way.
How It Works
Each unit is expressed as a fixed number of joules. The input is converted to joules first and then to every other unit, so you always see a consistent set of values.
- Joule, calorie, kWh and BTU
- Therm and foot-pound included
- Nutrition vs thermochemical calories
- Full conversion table
- Precision you control
Frequently asked questions
Why is a food Calorie 1000 calories?
A naming quirk. A physics calorie raises one gram of water by 1 °C, while the "Calorie" on a nutrition label is a kilocalorie — 1000 of them. The capital C is meant to signal the difference, but it is routinely lost in print.
How do kilowatt-hours relate to joules?
One kilowatt-hour is 3.6 megajoules — a kilowatt (1000 J per second) sustained for 3600 seconds. Electricity is billed in kWh because the numbers stay manageable: a joule is a very small amount of energy.
What is a BTU used for?
British thermal units measure the energy needed to heat one pound of water by 1 °F, and they survive mainly in air conditioning and heating, where equipment capacity is still quoted in BTU per hour.
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