About the Joules to Calories
This joules to calories converter changes an amount of energy in joules (J) into calories (cal) and kilocalories (kcal), and works in reverse too: pick calories, kilocalories, kilojoules or watt-hours as the starting unit and every other unit is filled in. A working line shows the division by 4.184 with your own number so you can copy it into homework or a lab report.
Physics and chemistry students use it for heat and specific-heat problems, athletes and dieters use it to make sense of energy figures quoted in joules, and engineers use it to compare heat output with electrical energy in watt-hours. Remember that the "Calorie" on a food label is a kilocalorie — 1,000 small calories — so 1 food Calorie is 4,184 joules.
The main result uses the thermochemical calorie (exactly 4.184 J), which is the definition used for nutrition labelling and most chemistry textbooks. The older International Table calorie (4.1868 J) is shown as a second output because some engineering and steam tables still use it; the two differ by about 0.07%.
With the default inputs, the calories is 239.0057 cal. Change any value above to recalculate instantly.
How to use the joules to calories
- 1Enter the amount of energy.
- 2Choose the unit you are converting from — joules by default.
- 3Read calories as the main result and kilocalories, kilojoules and watt-hours below it.
- 4Use the working line to show the calculation in homework or reports.
- 5Check the reference table for common values.
Formula and method
The thermochemical calorie is defined as exactly 4.184 joules, so dividing a number of joules by 4.184 gives calories, and multiplying calories by 4.184 gives joules. A kilocalorie (the food "Calorie") is 1,000 calories, so it equals 4,184 J or 4.184 kJ.
When you start from another unit, the tool first converts it to joules (1 kJ = 1,000 J, 1 Wh = 3,600 J) and then to every other unit. The International Table calorie of 4.1868 J is shown separately for engineering references that still use it.
- J
- Energy in joules (SI unit)
- cal
- Thermochemical calorie = 4.184 J
- kcal
- Kilocalorie or food Calorie = 1,000 cal = 4,184 J
- Wh
- Watt-hour = 3,600 J
Worked examples
1,000 joules to calories
1,000 ÷ 4.184 = 239.01 calories, or 0.239 kcal. Using the International Table calorie (4.1868 J) gives 238.85 cal, a difference of under 0.1%.
A 250 kcal snack in joules
250 kcal × 4,184 J = 1,046,000 J, which is 1,046 kJ — the figure you would see on an Australian or EU label. It is also about 290.6 Wh of energy.
5 kJ of heat
5 kJ is 5,000 J. Dividing by 4.184 gives 1,195.03 calories, or about 1.2 kilocalories.
Frequently asked questions
How many joules are in a calorie?+
One calorie (thermochemical) is exactly 4.184 joules. One kilocalorie, the food Calorie, is 4,184 joules or 4.184 kilojoules.
How do I convert joules to calories?+
Divide the number of joules by 4.184. For example, 500 J ÷ 4.184 = 119.5 cal. To get kilocalories, divide by 4,184 instead.
Is a food Calorie the same as a calorie?+
No. The capital-C Calorie on food labels is a kilocalorie, equal to 1,000 small calories or 4,184 J. A 200-Calorie snack therefore contains 836,800 joules.
What is the difference between the thermochemical and International Table calorie?+
The thermochemical calorie is 4.184 J and is used for nutrition and chemistry. The International Table calorie is 4.1868 J and appears in some engineering and steam tables. They differ by about 0.07%.
How many calories is 1 kJ?+
1 kilojoule is 1,000 ÷ 4.184 = 239.0 calories, or 0.239 kilocalories. To convert kJ on a food label to kcal, divide by 4.184.