Kilojoules to Kilocalories Converter

kcal

Common Conversions

kJ	kcal
1	0.239
4.184	1
10	2.39
25	5.975
50	11.95
100	23.9
250	59.75
500	119.5
890.3	212.8
1000	239
2000	478
5000	1195

Why this conversion matters in chemistry

Modern chemistry tables quote reaction enthalpies and bond energies in kJ/mol; biochemistry and a lot of molecular-dynamics tradition keeps using kcal/mol. The conversion is exact — 1 kcal = 4.184 kJ by definition of the thermochemical calorie. Methane's combustion enthalpy of −890 kJ/mol is also −213 kcal/mol, and either way the number says the same thing about how much energy a CH₄ molecule releases when it burns. Dividing by 4.184 is the step that lets an entry from one table sit next to an entry from the other without quietly being wrong by a factor of four.

Formula

kcal = kJ / 4.184

Worked Examples

4.184 kJ = 1 kcal

The definition line — one thermochemical kilocalorie is exactly 4.184 kJ.

285.8 kJ = 68.31 kcal

The enthalpy of combustion of hydrogen to liquid water, written in either energy unit.

890.3 kJ = 212.8 kcal

The enthalpy of combustion of methane — the reference reaction behind a lot of fuel-chemistry calculations.

2220 kJ = 530.6 kcal

Roughly the caloric content of a chocolate bar, where both SI and nutritional units show up on the same label.

Frequently Asked Questions

How do I convert kJ to kcal?

Divide by 4.184. So 100 kJ becomes 23.9 kcal. The factor is exact by definition, so no rounding sneaks in through the conversion itself.

Why do EU labels use kJ and US labels use Calories?

EU nutrition labels are SI-aligned and report energy in kilojoules. US labels use the nutritional Calorie, which is a kilocalorie. They describe the same energy content; the difference is one of unit convention, not caloric value.

Which unit do reaction enthalpies and bond energies use?

Modern inorganic, organic, and physical-chemistry references quote formation enthalpies and bond energies in kJ/mol. Older tables and most biochemistry work still use kcal/mol. Always confirm the convention of the source before combining values from two places.

Is one food Calorie the same as one kilocalorie?

Yes — the nutritional Calorie (capital C) equals one kilocalorie, which is 4.184 kJ or 4184 J. That's a routine source of confusion for students the first time they meet bomb calorimetry.