Joules to Calories

Joules and calories

The joule is the SI unit of energy: the work done by a force of one newton over one meter, or one watt for one second. Physics, engineering and EU food labels (as kJ) use joules.

The thermochemical calorie is exactly 4.184 joules, about the energy to warm 1 g of water by 1 °C. Chemistry uses small calories. Food "Calories" are kilocalories, a thousand times larger.

Worked example

Convert 1,000 J: 1,000 × 0.2390057361 = 239.0057361, so 1,000 joules is 239.0057361 calories. Likewise 2,000 J = 478.0114723 cal.

Estimating in your head

Divide by 4.2 for a quick figure; it is off by about 0.4%. For 1,000 J that gives 238 cal, against 239.006 exactly.

Going the other way

To convert calories to joules, divide by 0.2390057361 (or multiply by 4.184). The swap button between the boxes opens that page.

cal = J × 0.2390057361

1 J = 1 J and 1 cal = 4.184 J, both by definition, so the factor is their ratio: 0.2390057361 (rounded here; the page uses the full value). Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.