Kilojoules to calories

Multiply kilojoules by 239.0057 to get calories.

1 kJ = 239.0057 calNIST SP 811

Convert

4,780.1147cal

20 kJ = 4,780.1147 cal

How to convert kilojoules to calories

The calorie is the thermochemical calorie, exactly 4.184 joules. The kilojoule is one thousand joules — the metric food-energy unit used outside the US.

Worked example — 20 kJ: 20 × 239.0057 = 4,780.1147 cal.

Kilojoules to calories table

Common conversions.
Kilojoules	Calories
1 kJ	239.0057 cal
2 kJ	478.0115 cal
5 kJ	1,195.0287 cal
10 kJ	2,390.0574 cal
20 kJ	4,780.1147 cal
50 kJ	11,950.2868 cal
100 kJ	23,900.5736 cal
200 kJ	47,801.1472 cal
500 kJ	119,502.8681 cal

Reverse and related

kcal → kJ1 kcal = 4.184 kJ kJ → kcal1 kJ = 0.239006 kcal cal → J1 cal = 4.184 J J → cal1 J = 0.239006 cal kJ → J1 kJ = 1,000 J kWh → J1 kWh = 3,600,000 J

About kilojoules and calories

Kilojoule (kJ)

1 kJ = 239.0057 cal

Definition. One thousand joules — the metric food-energy unit used outside the US

History and origin

The kilojoule is one thousand joules, the metric unit of energy built on the SI joule. It is the food-energy unit preferred where the metric system is standard.

Current use

Kilojoules are used on nutrition labels outside the United States and throughout physics and engineering.

Source: NIST SP 811, Appendix B; ISO 80000-5 (energy)

Calorie (cal)

1 cal = 0.004184 kJ

Definition. The thermochemical calorie, exactly 4.184 joules

History and origin

The calorie was defined in the nineteenth century as the heat needed to raise one gram of water by one degree Celsius; the thermochemical calorie is now fixed at exactly 4.184 joules.

Current use

Calories are used in chemistry and to describe small amounts of energy; food labels use the larger kilocalorie.

Source: NIST SP 811, Appendix B; ISO 80000-5 (energy)

Where people use this

Kilojoules: nutrition labels outside the US, physics. Calories: chemistry, small energy amounts. 1 kJ is about 239 calories.

How we know this is right

The factor is fixed by the standards that define the units, not chosen — so it is exact, not a measurement:

1 cal = 0.004184 kJ, so 1 kJ = 1 ÷ 0.004184 = 239.0057 cal.

Every value is carried to full double precision; the display is rounded.

Both units are defined in NIST SP 811, Appendix B; ISO 80000-5 (energy).

Questions people ask

How many calories is 1 kJ?

One kilojoule is about 239 calories.

How many kJ is 1000 calories?

1000 calories is about 4.184 kJ.

Are these food Calories?

No — these are small calories; a food Calorie is a kilocalorie (1000 of them).

All kilojoule conversions

Kilocalories to kilojoules1 kcal = 4.184 kJ Kilojoules to kilocalories1 kJ = 0.239006 kcal Kilojoules to joules1 kJ = 1,000 J