Calories to Joules Converter
Type calories (small calories, as in chemistry) to get joules. One calorie is 4.184 J.
100 cal =
418.4J
100 calories is 418.4 joules.
- 1 cal
- 4.184 J
- 1 J
- 0.239 cal
How to convert calories to joules
Multiply the number of calories by 4.184. In chemistry and physics a calorie (small c) is roughly the heat that warms one gram of water by one degree Celsius, and it is now defined as exactly 4.184 joules (the thermochemical calorie).
Melting one gram of ice takes about 80 calories: 80 × 4.184 = 334.7 J, which matches the 334 J/g usually quoted for the heat of fusion of water.
Some older tables use the International Table calorie, 4.1868 J. The two differ by only 0.07%, but check which one a textbook means before comparing answers to four figures.
joules = calories × 4.184
- NIST lists the thermochemical calorie as exactly 4.184 J and the International Table calorie as exactly 4.1868 J. Source: NIST SP 811, Appendix B.8: conversion factors by unit.
How to estimate calories to joules in your head
Multiply by 4 and add a little under 5%. 50 calories × 4 = 200, plus 9 gives 209, and the exact answer is 209.2 J. For homework, write the full 4.184 anyway; it is exact.
Calories to joules table
Small calories (cal), as used in chemistry and heat problems, in joules.
| Calories (cal) | Joules (J) | Example |
|---|---|---|
| 1 | 4.184 | warms 1 g of water by about 1 °C |
| 2 | 8.368 | |
| 5 | 20.92 | |
| 10 | 41.84 | |
| 15 | 62.76 | |
| 20 | 83.68 | |
| 25 | 104.6 | |
| 50 | 209.2 | |
| 75 | 313.8 | |
| 80 | 334.72 | melts about 1 g of ice |
Show all 18 rowsShow fewer
| 100 | 418.4 | |
| 150 | 627.6 | |
| 200 | 836.8 | |
| 250 | 1,046 | |
| 500 | 2,092 | |
| 540 | 2,259.36 | boils off about 1 g of water at 100 °C |
| 750 | 3,138 | |
| 1,000 | 4,184 | one food Calorie (1 kcal) |
Frequently Asked Questions
How many joules is 100 calories?
100 small calories is 418.4 J. If you mean 100 food Calories (kcal), it is a thousand times more: 418,400 J, or 418.4 kJ.
Is a calorie in physics the same as a calorie on food?
No. A food Calorie is a kilocalorie, 1,000 of the small calories used in physics and chemistry. Both rest on the same 4.184 J definition.
How many calories are in a joule?
One joule is 1 ÷ 4.184 = 0.239 calories, roughly a quarter of a calorie. So 1,000 J works out to 239 cal.
How much energy does it take to heat a cup of water?
Warming 250 g of water by 20 °C takes about 250 × 20 = 5,000 calories, which is 20,920 J or roughly 21 kJ.