Heat Capacity Converter

Heat Capacity Converter – J/K, BTU/°F, cal/K and More

The Heat Capacity Converter instantly converts heat capacity and specific heat capacity values between the SI, CGS, imperial, and energy-based units used across thermodynamics, HVAC engineering, materials science, and chemistry. Whether you need to convert J/K to BTU/°F for a US engineering spec, or cal/(g·°C) to kJ/(kg·K) for a lab report, this tool delivers accurate results instantly with an optional all-units reference table.

All conversions run entirely in your browser — no sign-up or installation required, and results update automatically as you type.

Heat Capacity vs Specific Heat Capacity

Heat capacity (symbol C, unit J/K) is the amount of heat energy required to raise the temperature of an entire object by one kelvin. It depends on both the material and the mass of the object — a large block of steel has a much higher heat capacity than a small one, even though both are steel.

Specific heat capacity (symbol c, unit J/(kg·K)) is the heat capacity per unit mass — an intrinsic property of the material itself, independent of how much of it you have. The relationship between the two is:

where C is total heat capacity (J/K), m is mass (kg), and c is specific heat capacity (J/(kg·K)). Because these two quantities belong to different unit families, this converter offers separate modes for each — converting within the total heat capacity family or within the specific heat family, without requiring you to supply a mass value.

Supported Units

SI and Metric Units

• J/K— The SI unit of heat capacity. 1 J/K means 1 joule of heat is needed to raise the object's temperature by 1 kelvin.
• kJ/K — 1,000 J/K. Common for larger objects and industrial thermal masses.
• J/(kg·K) and kJ/(kg·K) — SI specific heat units. Water has a specific heat of about 4,186 J/(kg·K) or 4.186 kJ/(kg·K).

CGS Units

• cal/K (equal to cal/°C) — 1 cal/K = 4.1868 J/K, using the thermochemical calorie. Common in chemistry coursework.
• kcal/K (equal to kcal/°C) — 1 kcal/K = 4,186.8 J/K. Used in food science and process engineering.
• cal/(g·°C) and kcal/(kg·°C) — By definition, water has a specific heat capacity of almost exactly 1 cal/(g·°C), making this a convenient reference unit.

Imperial / US Units

• BTU/°F — The standard imperial heat capacity unit used in US HVAC and engineering. 1 BTU/°F ≈ 1,899.1 J/K.
• BTU/°R — Numerically identical to BTU/°F, since a Rankine degree and a Fahrenheit degree are the same size.
• ft·lbf/°F — A mechanical-energy-based imperial unit. 1 ft·lbf/°F ≈ 2.287 J/K.
• BTU/(lb·°F) — The imperial specific heat unit, numerically equal to cal/(g·°C) at roughly 4,186.8 J/(kg·K).

Energy-based Units

• Wh/K — 1 Wh/K = 3,600 J/K, since 1 watt-hour equals 3,600 joules. Useful when relating heat capacity to battery or electrical thermal mass.
• kWh/K — 1 kWh/K = 3,600,000 J/K. Used for large thermal storage systems such as HVAC buffer tanks.

How the Conversion Works

Every total heat capacity conversion normalises through J/Kin two steps: the input value is multiplied by the source unit's conversion factor to obtain the J/K equivalent, then divided by the target unit's factor to produce the result. Specific heat conversions follow the identical process using J/(kg·K) as the base.

Example — converting 4186 J/K to cal/K:

• 4186 J/K × 1 [already in base] = 4186 J/K
• 4186 J/K ÷ 4.1868 [cal/K factor] = 999.95 cal/K

Example — converting 1000 J/K to BTU/°F:

• 1000 J/K ÷ 1899.1008 [BTU/°F factor] = 0.5266 BTU/°F

Practical Applications

• Thermodynamics coursework: Students frequently need to convert between SI joules-based units and the calorie-based units used in classic textbook problems.
• HVAC and building engineering: US specifications often use BTU/°F for system thermal mass, while international standards use J/K or kJ/K.
• Materials science and chemistry:Specific heat capacity values for new materials are often reported in cal/(g·°C) or J/(kg·K) depending on the publication's region and era.
• Energy storage analysis: Relating thermal mass to electrical energy storage (Wh/K, kWh/K) is useful when sizing battery enclosures or thermal buffer systems.
• Process and food engineering: Kilocalorie-based units remain common in food science specifications and some process engineering documentation.

Tips for Using This Converter

• Use the Conversion Mode toggle to switch between total heat capacity (J/K family) and specific heat capacity (J/(kg·K) family) — choosing the wrong family for your data will produce a unit mismatch.
• Enable Show all unit conversions in total heat capacity mode to see your value expressed in every supported unit simultaneously, grouped by measurement system.
• Use the Swap button to quickly reverse the conversion direction and verify a round-trip calculation.
• Increase the decimal places setting when working with very small specific heat differences, such as comparing similar alloys or polymer formulations.