Convert specific heat between J/(kg·K), kJ/(kg·K), cal/(g·°C) and BTU/(lb·°F).
Heat • 6 units
All 6 units on the Specific Heat Capacity Converter are defined against the Joule/(kg·K) (J/(kg·K)), so each result is one conversion factor away from a single reference rather than the end of a chain of roundings.
The conversion this page is most often opened for is ready before you type anything: 1 J/(kg·K) = 0.0002388459 BTU/(lb·°F). Change either side and every row in the table recalculates with it.
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The conversion from SI is small enough to be worth memorising as a reciprocal: 1 J/(kg·K) is 2.3885 × 10⁻⁴ BTU/(lb·°F), so multiplying by 4,186.8 goes the other way. The arithmetic that uses it is short — energy equals mass times specific heat times temperature rise — and the numbers grow quickly. Heating a 200-litre cylinder of water from 15 °C to 60 °C takes about 37.7 MJ, or 10.5 kWh, which is why domestic hot water is such a large share of a household energy bill.
Gases require a distinction that solids and liquids do not. A gas heated at constant pressure does work as it expands, so it absorbs more energy than the same gas heated at constant volume: air is about 1,005 J/(kg·K) at constant pressure against 718 at constant volume, a ratio of roughly 1.4 that reappears throughout compressible-flow and engine analysis. For liquids and solids the two values differ so little that tables rarely bother to say which is quoted, but for a gas an unlabelled figure is ambiguous.
Where space rather than mass is the constraint, the quantity to compare is volumetric heat capacity — specific heat multiplied by density. Water stores about 4.18 MJ per cubic metre per kelvin against roughly 2.1 for concrete, so water wins on both a per-kilogram and a per-litre basis, which is what makes it the default thermal store. Specific heat also drifts with temperature, so a value taken from a table at room temperature will not describe the same substance in a furnace or a cryostat.
Quick reference — 1 Joule/(kg·K) (J/(kg·K)) is equal to:
| Kilojoule/(kg·K) | kJ/(kg·K) | 0.001 |
| Joule/(g·K) | J/(g·K) | 0.001 |
| Calorie/(g·°C) | cal/(g·°C) | 0.0002390057 |
| Kilocalorie/(kg·°C) | kcal/(kg·°C) | 0.0002390057 |
| BTU/(lb·°F) | BTU/(lb·°F) | 0.0002388459 |
6 units of specific heat capacity, each a fixed multiple of the J/(kg·K). The table spans 4,187:1, from J/(kg·K) (1 J/(kg·K)) to BTU/(lb·°F) (4186.8 J/(kg·K)). Conversion is one multiplication into the base unit and one division out of it, with no lookup table and no approximation.
value_to = value_from × (factor_from ÷ factor_to)1 J/(kg·K) = 1 J/(kg·K)1 kJ/(kg·K) = 1000 J/(kg·K)1 J/(g·K) = 1000 J/(kg·K)1 cal/(g·°C) = 4184 J/(kg·K)1 kcal/(kg·°C) = 4184 J/(kg·K)1 BTU/(lb·°F) = 4186.8 J/(kg·K)where:
Assumptions: Factors are exact definitions. Full double precision is carried internally and rounding is applied only for display.
Result25 J/(kg·K) = 0.00597115 BTU/(lb·°F)
Specific heat capacity is the energy needed to raise one kilogram of a substance by one kelvin, in J/(kg·K). Water's value of about 4,184 J/(kg·K) is remarkably high — roughly ten times that of copper and four times that of dry air by mass — which is why it remains the default coolant and thermal store in almost every application.
The unit itself carries a historical trap. The calorie was defined so that water's specific heat is exactly 1 cal/(g·°C), which makes the conversion factor 4,184 rather than a round number, and the imperial BTU/(lb·°F) happens to be numerically identical to cal/(g·°C). Two of the three unit systems agree by construction and the SI one does not, which is exactly the sort of coincidence that produces confident wrong answers.