Energy Converter — Joules, Calories, kWh & BTU

Convert between joules, calories, kilowatt-hours, BTU, foot-pounds, and electronvolts using NIST SP 811 factors.

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How this conversion works. Every unit is converted through the joule (SI) with conversion factors from NIST Special Publication 811.

How to use

  1. Pick the unit you are converting from, such as Joule (J) or Kilojoule (kJ).
  2. Type the value and every other unit updates as you type.
  3. Copy the figure you need, or use the swap button to reverse the direction, Electronvolt (eV) included.

Frequently asked questions

How do I convert kilocalorie / food calorie to kilojoule?

1 kilocalorie / food calorie = 4.184 kilojoule. Choose "Kilocalorie / food Calorie (kcal)" as From and "Kilojoule (kJ)" as To, type a value, and the result updates instantly.

Are food Calories the same as calories?

A food Calorie (capital C, on nutrition labels) is one kilocalorie = 4,184 J. The small thermochemical calorie is 4.184 J — a factor of 1,000 apart.

How many BTU are in a kWh?

1 kWh = 3,412.14 BTU (International Table). HVAC equipment is rated in BTU/h; multiply by run hours and divide by 3,412 to estimate kWh consumption.

Is my data sent to a server?

No. Conversions run entirely in your browser using fixed factors — nothing is uploaded or logged.

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