Specific Heat Capacity Converter
Same value in every unit
| Unit | Value |
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Energy per kilogram, per degree
Specific heat capacity answers one question: how much energy does it take to raise a kilogram of something by one degree? The working relationship is Q = m × c × ΔT — energy equals mass times specific heat times temperature change. Keep mass in kilograms, c in J/(kg·K) and ΔT in degrees, and Q comes out in joules. Heating one litre of water from 20 °C to 100 °C is 1 × 4186 × 80, or about 335 kJ.
Water is the outlier
At roughly 4186 J/(kg·K), liquid water stores far more heat per kilogram than almost anything else you will meet. That is why the sea moderates coastal climate, why water is the default coolant in engines and data centres, and why a hot water bottle stays warm for hours. The advantage shrinks if you compare by volume rather than by mass: multiply by density and water gives about 4.19 MJ/(m³·K) against about 3.45 MJ/(m³·K) for copper, so an eleven-fold lead per kilogram becomes only about 1.2-fold per cubic metre.
- Liquid water — about 4186 J/(kg·K)
- Ice — about 2100 J/(kg·K)
- Air at constant pressure — about 1005 J/(kg·K)
- Aluminium — about 900 J/(kg·K)
- Glass — about 840 J/(kg·K)
- Iron — about 450 J/(kg·K)
- Copper — about 385 J/(kg·K)
- Lead — about 128 J/(kg·K)
Treat these as room-temperature approximations. Real values shift with temperature — water itself is about 4217 J/(kg·K) at 0 °C — and for alloys they shift with composition too.
Why two of these units read as 1.00 for water
The imperial and calorie units were built around water. A BTU was originally the heat needed to raise a pound of water by one degree Fahrenheit; a calorie the heat needed to raise a gram of water by one degree Celsius. Water therefore lands at essentially 1.00 in both BTU/(lb·°F) and cal/(g·°C), which makes a table in either unit read as a ratio against water. Both are now defined as fixed numbers of joules, and two rival calorie definitions survive — which is why this page uses 4186.8 J/(kg·K) for BTU/(lb·°F) and 4184 for cal/(g·°C), about 0.07% apart.
Two things that catch people out
A temperature difference is not a temperature. Adding 273.15 when converting a ΔT from Celsius to kelvin is a common error in this calculation: an 80-degree rise is 80 K, full stop. Second, for gases check whether your source quotes the constant-pressure or the constant-volume value before converting. For air, cp is about 40% larger than cv, and no unit converter can tell them apart.
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Frequently Asked Questions
Liquid water is about 4186 J/(kg·K) near room temperature, which is roughly 4.19 kJ/(kg·K) and essentially 1.00 in both BTU/(lb·°F) and cal/(g·°C). That is unusually high — most metals sit well below 1000 J/(kg·K), with copper around 385. The exact figure moves with temperature: sources quote roughly 4179 to 4187 J/(kg·K) across the usual 10–40 °C range, rising to about 4217 at 0 °C. That whole spread is under 1%, so it rarely matters outside precise work.
Because those units were defined around water. A BTU was originally the heat needed to raise one pound of water by one degree Fahrenheit, and a calorie the heat needed to raise one gram of water by one degree Celsius, so water necessarily comes out near 1.00 in each. The two factors on this page differ slightly — 4186.8 against 4184 J/(kg·K), about 0.07% — because they rest on different calorie definitions: the International Table calorie of exactly 4.1868 J sits behind the BTU figure, while cal/(g·°C) here uses the thermochemical calorie of exactly 4.184 J.
Yes, for specific heat they are interchangeable. The unit describes a change in temperature, and one kelvin and one degree Celsius are exactly the same size of interval. A value of 4186 J/(kg·K) is also 4186 J/(kg·°C). The trap is in the ΔT you multiply by: a temperature difference is already the same number in both scales, so never add 273.15 to it.
Taking one litre (about 1 kg) from 20 °C to 100 °C needs about 335 kJ: 1 × 4186 × 80. That is 0.093 kWh, so a perfectly efficient 2 kW kettle would need about 167 seconds. Note that this only brings the water to boiling point — actually turning that kilogram into steam requires about 2.26 MJ more as latent heat of vaporisation, which specific heat capacity does not cover. Real kettles also lose heat to the vessel and the air, so allow more than the ideal figure.
Because the kilo prefixes cancel. Going from calories to kilocalories divides by 1000, and going from grams to kilograms multiplies by 1000, so the two are the same quantity written differently — both 4184 J/(kg·K). Chemistry texts tend to use cal/(g·°C) while food science and older engineering tables prefer kcal/(kg·°C), but no conversion is needed between them.
For most practical work you want cp, the constant-pressure value, which is about 1005 J/(kg·K) for air against roughly 718 J/(kg·K) for cv at constant volume — a ratio of about 1.4. Use cp when the gas is free to expand: flow through a duct, a heat exchanger, a room being heated. Use cv for a sealed rigid volume. A converter only changes units, so identify which value your source figure is before you convert it.