The calorie-to-joule conversion is one of the most common energy conversions in physics and chemistry. One small calorie equals 4.184 joules exactly. This converter turns the gram-calorie (lowercase c) into joules — the SI unit of energy — and back again, instantly and in your browser. It is built for lab work, homework and textbook problems, not nutrition labels.
How it works
The tool multiplies by a single exact constant. To go from calories to joules it computes J = cal × 4.184; to reverse it, cal = J ÷ 4.184. The 4.184 figure is the definition of the thermochemical calorie, so the conversion is exact rather than approximate. Be careful not to confuse this small calorie with the food Calorie (capital C) on nutrition labels, which is a kilocalorie equal to 1,000 small calories, or 4,184 J.
Reference table
| Calories (cal) | Joules (J) |
|---|---|
| 1 | 4.184 |
| 10 | 41.84 |
| 100 | 418.4 |
| 500 | 2,092 |
| 1,000 | 4,184 |
When you actually need this conversion
The small (thermochemical) calorie appears in several practical contexts:
- Chemistry homework and lab reports — heats of combustion, enthalpy changes, and specific heat capacity problems are often given in cal or cal/g·°C and need converting to the SI joule.
- Thermodynamics textbooks — older engineering references quote heat in calories or BTU; converting to joules aligns results with SI.
- Calorimetry — measuring the heat released by a reaction in a bomb calorimeter often produces results in calories that must be reported in joules for a journal.
- Physics problem sets — specific heat, latent heat, and work-energy problems sometimes mix units from different systems.
The capital-C Calorie trap
The most common mistake is confusing the small calorie (cal) with the food Calorie (Cal or kcal). A nutrition label showing “200 Calories” means 200 kilocalories — 200,000 small calories — or 836,800 joules. If you are working with food energy and need to convert to joules, first confirm whether the value is in kcal or cal, then use J = kcal × 4,184. This converter handles the small calorie only.
Other calorie definitions
The thermochemical calorie (4.184 J) used here is the standard in chemistry. A slightly different value — 4.1868 J — is the International Table calorie, which appears in some steam-table engineering references. The difference is about 0.07%, negligible for most purposes, but worth knowing if your textbook or reference uses the IT calorie specifically.
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