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Joules to Calories Converter
↔ Convert cal to J instead

Common Conversions

J cal
1 0.239
4.184 1
10 2.39
50 11.95
100 23.9
500 119.5
1000 239
4184 1000
10000 2390
50000 11950
100000 23900

Why this conversion matters in chemistry

Modern calorimetry measurements come out in joules directly — the electronics measure heat-capacity times temperature change in SI units, so joules fall out naturally. The trouble comes when those values have to be compared against older thermochemical tables, which list combustion enthalpies in cal/mol or kcal/mol. A benzoic-acid calibration standard at 26.434 kJ/g only matches the tabulated 6318 cal/g if you apply the exact 4.184 factor. Drop the division and a calibration discrepancy reads like instrument drift when it's really just unit bookkeeping. The conversion is a divide by 4.184 — an exact number, defined that way since the 1956 redefinition of the thermochemical calorie.

Formula

cal = J ÷ 4.184

Worked Examples

4.184 J = 1 cal

The defining equivalence. The thermochemical calorie is exactly 4.184 J by international agreement.

4184 J = 1000 cal

One kilocalorie — and also one food-label "Calorie," capital C. Worth keeping this equivalence handy for any conversation involving nutrition data.

100 J = 23.9 cal

A small energy change, of the kind you'd see from a minor temperature shift in a coffee-cup calorimeter.

285800 J = 68310 cal

Heat released by combusting a mole of H₂ — 68.3 kcal/mol. A standard reference value in thermochemistry courses.

Frequently Asked Questions

How do I convert joules to calories?
Divide by 4.184. So 100 J becomes 23.9 cal, 1000 J becomes 239 cal. The factor is exact by definition of the thermochemical calorie — no rounding trade-off to worry about.
What's the difference between calorie (cal) and Calorie (Cal)?
A lowercase cal is 4.184 J — the scientific unit. An uppercase Cal (or kcal) is 1000 cal, or 4184 J — what food labels use. The naming overlap is historical and more than a little confusing; in chemistry, "calorie" almost always means the thermochemical calorie, not the food-label unit.
Why do older chemistry references use calories?
American thermochemistry grew up around the calorie long before SI became universal. Older textbooks, pre-1970 NBS reference tables, and much of mid-century biochemistry literature report enthalpies in kcal/mol. The SI convention has dominated since around 1960, but both notations persist in the literature.
What's the specific heat of water in calories?
Exactly 1 cal/(g·°C), by the original definition of the calorie. In SI units that's 4.184 J/(g·°C). The clean "1" in calories is why the unit survived so long in thermochemistry — calorimetry calculations simplified nicely as long as water was the working fluid.