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Kilocalories to Joules Converter
↔ Convert J to kcal instead

Common Conversions

kcal J
0.001 4.184
0.01 41.84
0.1 418.4
1 4184
5 20920
10 41840
25 104600
50 209200
100 418400
250 1046000
500 2092000
1000 4184000

Why this conversion matters in chemistry

Bond energies, activation barriers, and reaction enthalpies in older biochemistry and physical-chemistry literature run in kcal/mol. Molecular-dynamics force fields, modern thermodynamic data tables, and SI-aligned process work prefer joules. A 10 kcal/mol activation barrier is 41,840 J/mol, the value an MD simulation's free-energy input file actually wants. Multiplying by 4184 is the ordinary step that lets a generation of biochemistry data meet a modern computational-chemistry calculation. The factor is exact through the IUPAC thermochemical calorie definition.

Formula

J = kcal × 4184

Worked Examples

1 kcal = 4184 J

The defining identity of the thermochemical kilocalorie.

100 kcal = 418400 J

About the energy content of a typical small snack — the same value as 100 Calories on a US food label.

57.8 kcal = 241800 J

The standard enthalpy of formation of gaseous water (magnitude only; the actual value is negative).

0.001 kcal = 4.184 J

One thermochemical calorie — the small-cal unit that food labels collapse into the kcal scale.

Frequently Asked Questions

How do I convert kcal to J?
Multiply by 4184. So 10 kcal becomes 41,840 J, equivalently 41.84 kJ. The factor is exact through the thermochemical calorie definition (1 cal = 4.184 J).
What's the difference between cal, kcal, and Cal?
1 cal (small calorie) = 4.184 J. 1 kcal = 1000 cal = 4184 J. 1 Cal (dietary Calorie, capital C) = 1 kcal. So a food label showing 100 Calories means 100 kcal — equivalently 418,400 J. The capitalization carries a thousand-fold meaning.
Why do older chemistry tables use kcal?
Before SI took over, the calorie was the standard thermochemical energy unit. Pre-1970s references — many still in active use — report ΔH, ΔG, and bond energies in kcal/mol. Converting to kJ/mol is just multiplying by 4.184.
How do kcal/mol and kJ/mol compare?
1 kcal/mol equals 4.184 kJ/mol exactly. So a 99 kcal/mol C–H bond energy lands at about 414 kJ/mol in modern SI tables — same physics, different unit convention.