Kilocalories to kilojoules converter

How to convert kcal to kJ

Multiply the kilocalories by 4.184: kJ = kcal × 4.184. A 250 kcal snack is 1,046 kJ, and the 2,000-Calorie diet that US labels base their daily values on is 8,368 kJ. The factor is exact for food Calories, which are kilocalories, and for chemistry data in kcal.

Why 1 kcal is exactly 4.184 kJ

The calorie used in nutrition and chemistry, the thermochemical calorie, is defined as exactly 4.184 joules (NIST). A kilocalorie is 1,000 of them and a kilojoule is 1,000 joules, so the prefixes cancel.

A kilojoule is the smaller unit, so the kJ figure is always a little over four times the kcal figure. An answer smaller than the number you started with means you divided instead of multiplying.

Worked examples

• 100 kcal: 100 × 4.184 = 418.4 kJ
• A 500 kcal meal: 500 × 4.184 = 2,092 kJ
• A 14,000 kcal week: 14,000 × 4.184 = 58,576 kJ

To do it in your head, multiply by 4 and add 4.6% of the result. For 250 kcal, 250 × 4 = 1,000 and 4.6% of 1,000 is 46, giving 1,046 kJ. The shortcut is exact because 4 × 1.046 = 4.184.

kcal to kJ chart

Are food Calories the same as kcal?

Yes. US Nutrition Facts labels list Calories, and each food Calorie is one kilocalorie. A 150-Calorie serving is 150 kcal, or 627.6 kJ, the number to compare with a label that gives energy in kJ.

A lowercase calorie (cal) is 1,000 times smaller. 250 cal is 0.25 kcal, which is 1.046 kJ; reading it as 250 kcal gives 1,046 kJ, a thousand times too much.

Converting kcal/mol to kJ/mol

Older thermochemistry tables give reaction enthalpies in kcal/mol, based on the same thermochemical calorie. Multiply by 4.184 and keep the per-mole basis: −10 kcal/mol is −41.84 kJ/mol.

Common mistakes

• Rounding the factor to 4.2. Fine for a rough estimate, but 250 kcal becomes 1,050 kJ instead of 1,046 kJ, 4 kJ too high, and a 14,000 kcal week comes out 224 kJ high.
• Using a different calorie. Some engineering sources use the International Table calorie of 4.1868 J. On that basis 1,000 kcal is 4,186.8 kJ instead of 4,184 kJ, so check which calorie a technical source means.
• Converting a rate as an amount. kcal/h measures power, not energy. Use the power converter for it: 100 kcal/h is about 116.2 W.

Related conversions

Use kJ to kcal for the reverse step and the energy converter for joules, watt-hours or BTU. To estimate how many kcal you need a day, see the calorie and macro calculator.