About the Calories to Joules Converter
Physics and chemistry measure heat in joules, while older books, labs and some labels still use calories. This converter turns calories into joules using the thermochemical calorie, defined as exactly 4.184 joules. Type a number of calories and the joules appear immediately, with kilojoules, kilocalories, watt-hours, kilowatt-hours, BTU and other units listed below. It is meant for the small calorie, written cal. Food labels use the large Calorie, which is a kilocalorie, so 1 food Calorie is 4,184 joules. Use the kcal rows to see that value, and everything is worked out in your browser without sending your numbers anywhere.
Updated October 2026
How to use the Calories to Joules Converter
- 1Type the number of calories (cal).
- 2Read the joules at the top of the result.
- 3See kilojoules and kilocalories in the rows below.
- 4Press Copy to copy the sentence, for example 100 cal = 418.4 J.
- 5Change the number for another amount.
The formula
joules = calories × 4.184. The factor is exact because the thermochemical calorie is defined that way: the heat to warm one gram of water by one degree Celsius is about one calorie.
To go the other way, divide joules by 4.184 with the Joules to Calories converter.
Examples
- 1 cal = 4.184 J
- 100 cal = 418.4 J
- 1,000 cal (1 kcal) = 4,184 J = 4.184 kJ
- 2,000 kcal, a common daily food energy figure, = 8,368 kJ
Where you meet calories
Chemistry labs report heats of reaction and heat capacities in calories or joules. Specific heat of water is 4.184 J per gram per degree, or 1 cal per gram per degree. Food packets in many countries show both kcal and kJ, and the conversion is the one used here.
If you are converting nutrition values, remember that a food Calorie is 1,000 of these calories.
Which calorie do you mean?
Three things are called a calorie. The small calorie, written cal, is about 4.184 J and is what this page converts. The kilocalorie, written kcal or Cal, is 1,000 small calories and is the food calorie. The International Table calorie of 4.1868 J is used in some engineering tables.
If a recipe, a watch or a food label says 250 calories, it almost certainly means 250 kilocalories. Enter 250,000 here to convert it, or use the kcal row on the Joules to Calories page. For heat in a lab, such as warming 100 g of water by 5 degrees, 500 cal or 2,092 J is the right figure.
Phone and computer
The input and the result sit side by side on a computer and stack on a phone. Calories and joules both measure energy, but food labels and physics books use them differently. Convert the other way with the Joules to Calories Converter, use the Calorie Calculator to estimate how many you need each day, and the Specific Heat Calculator to see how much heat warms a material.
Features
- Thermochemical calorie, exactly 4.184 J
- Kilojoules, kilocalories, watt-hours and BTU shown together
- Handles tiny and large numbers
- Ten significant digits
- Copy button
- Private, runs in your browser
Frequently asked questions
How many joules are in a calorie?
One calorie (cal) is exactly 4.184 joules in the thermochemical definition.
What is the difference between a calorie and a Calorie?
A calorie, with a small c, is 4.184 J. A food Calorie, with a capital C, is a kilocalorie, which is 1,000 calories or 4,184 J.
Are there other definitions of the calorie?
Yes. The International Table calorie is 4.1868 J and the 15 degree calorie is about 4.1855 J. They differ by less than 0.1 percent. This tool uses 4.184 J, the one used in chemistry and nutrition.
How do I convert by hand?
Multiply the calories by 4.184. For example 250 cal is 1,046 J.
How do I convert kcal to joules?
Multiply by 4,184, or enter the kilocalories times 1,000 here. See the kcal row for the reverse.
How many kilojoules is that?
Divide the joules by 1,000. The kJ row shows it for you.
Is my data sent anywhere?
No. It is worked out in your browser.