Convert between joules, calories, kilowatt-hours, BTU, electronvolts and other energy units.
Energy is the same physical quantity whether it is heating water, spinning a motor or accelerating a particle, but the units it is measured in reflect the field that uses it. A nutritionist measures food energy in kilocalories, an electrician bills in kilowatt-hours, a mechanical engineer works in joules or foot-pounds, and a physicist studying atomic transitions uses electronvolts. They are all conversion factors away from each other, and this page does the arithmetic.
The joule is the SI base unit, so every other unit here is defined as a fixed multiple of it: 1 kcal = 4184 J, 1 kWh = 3.6 × 10⁶ J, 1 BTU = 1055.06 J, 1 eV = 1.602 × 10⁻¹⁹ J. The conversions are exact definitions, not measurements, so the numbers on this page are as precise as the definitions themselves.
One common source of confusion: a food calorie (the one on nutrition labels) is actually a kilocalorie, 1000 thermochemical calories. This page lists both, so you can see the factor of 1000 between them. Everything runs in your browser — the value you type is not uploaded or stored.
value_in_target = value_in_source × (source_factor / target_factor), where each factor is the number of joules in one unit.
A factor of 1000. The "calorie" on food labels is a kilocalorie (kcal). The thermochemical calorie (cal) is 1000 times smaller. This page lists both.
Because it is the energy of a single electron accelerated through one volt — a quantity relevant to atomic physics. In everyday terms, 1 eV is about 1.6 × 10⁻¹⁹ J.
Multiply kWh by 3,600,000. One kilowatt-hour is 3.6 megajoules.
No. The conversion runs in JavaScript on your device.
Yes. Each unit is defined as a fixed number of joules, so the conversions are definitions, not approximations.
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