Express the same energy in another unit

A battery and a heated vessel joined by conversion arrows

Enter energy in either field and select two units. The other field updates immediately, whether the value starts in joules, kilowatt-hours, calories, Btu, or a conventional fuel equivalent.

Every conversion passes through joules

The converter assigns each unit a factor in joules. It multiplies the source value by its factor, then divides by the target factor.

E_2=E_1\times\frac{k_1}{k_2}

Here E is the numerical energy value and k is the number of joules in one unit. For example, 1 Wh is 3,600 J because one watt means one joule per second and one hour contains 3,600 seconds. NIST lists the standard conversion factors for units used with SI.

Useful checks across three scales

Electricity: 1 kWh equals 3.6 MJ. A 2 kW appliance running for half an hour therefore uses 1 kWh, assuming the power stays constant.

Food energy: 500 thermochemical kcal equals 2.092 MJ. The number 500 on a food-energy label normally refers to kilocalories, not 500 small calories.

Engineering comparison: 1 kg of TNT equivalent equals 4.184 MJ. This is a defined comparison unit; it does not describe the mass of an unknown explosive.

Exact factors and conventional equivalents

Metric prefixes and watt-hour relationships are exact here. The converter uses the thermochemical calorie, 4.184 J, and the International Table Btu, 1,055.05585262 J. Different historical calorie or Btu definitions produce slightly different answers, so the unit name matters.

A tonne of oil equivalent and a barrel of oil equivalent are standardized comparison quantities. Real fuel samples vary in composition and heating value. The display keeps up to 12 significant digits, but extra digits do not make an approximate fuel equivalent more certain.

Questions about energy conversion

Most mistakes come from confusing energy with power or small calories with food kilocalories.

Is a kilowatt the same as a kilowatt-hour?

No. A kilowatt measures power, while a kilowatt-hour measures energy used or delivered over time.

How many joules are in 1 kWh?

Exactly 3,600,000 J, which is also 3.6 MJ.

Does kcal mean the Calories shown on food labels?

Usually yes. One nutritional Calorie with a capital C is one kilocalorie, or 4,184 J in the thermochemical definition used here.

Can I type into the converted field?

Yes. Both fields are editable, and the last field changed becomes the source for the next conversion.

Does the converter include efficiency or heat loss?

No. It changes the unit only. Equipment efficiency and losses require a separate calculation.

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Calcopedia (en) → Energy unit converter