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Joule Converters

Convert joules to calories, BTU, watt-hours, kilowatt-hours and other energy units for physics and engineering.

What this tool does

Convert joules to calories, BTU, watt-hours, kilowatt-hours and other energy units for physics and engineering. Type an amount in joules, choose the units, and the tool converts it to calories (thermochemical). It offers 18 energy units and also shows the same amount in the others.

Inputs

  • Value: A number.
  • From: Choose one from 18 options, including Joule, Kilojoule, Megajoule, Gigajoule, Millijoule, Calorie (thermochemical). Starts as Joule.
  • To: Choose one of the same 18 units as "From". Starts as Calorie (thermochemical).

How to use

  1. Enter the amount you want to convert.
  2. Choose the unit to convert from and the unit to convert to.
  3. Read the result: the converted amount and the same amount in the other units. It appears once every required field has a valid value.

Worked examples

Conversions from joules to calories (thermochemical):

  • 1 J ≈ 0.239006 cal (th)
  • 5 J ≈ 1.195029 cal (th)
  • 10 J ≈ 2.390057 cal (th)
  • 50 J ≈ 11.950287 cal (th)
  • 100 J ≈ 23.900574 cal (th)

Multiply the number of joules by about 0.239006 to get calories (thermochemical). The factor follows from exact definitions. It has more digits than fit here, so it is shown rounded.

Sources: Joule: SI Brochure, 9th edition (2019). Calorie (thermochemical): NIST SP 811 (2008), Appendix B.8.

Limitations

  • Converts energy units only. It does not convert power, such as watts, or work out cost.
  • Calories, BTU and therms have several definitions, so check the label of the one you need.

FAQs

Q: How many joules are in a calorie?
A: A thermochemical calorie is exactly 4.184 J. The International Table calorie is exactly 4.1868 J. Both are listed, and the page starts with the thermochemical one.
Q: Is the food Calorie the same as a calorie?
A: A food Calorie is a kilocalorie, which is 1,000 calories. Use the kilocalorie rows for nutrition labels.
Q: Why are there several BTU and therm entries?
A: Different standards define the BTU and the therm slightly differently. Each variant is labelled so you can pick the one your source uses.

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