Thermal Conductivity Converter

Thermal conductivity (k, or λ) is how well a material conducts heat: the heat that flows each second through a layer one unit thick and one unit in area, for each degree of temperature difference across it. Its SI unit is the watt per meter per kelvin, W/(m·K).

Copper conducts about 400 W/(m·K), steel about 50, glass about 1, and mineral wool insulation about 0.04. A temperature difference of 1 K is the same as one of 1 °C, so W/(m·K) and W/(m·°C) are the same number.

How to convert thermal conductivity units

Type a value into any field, and every other unit is calculated at once. For example, steel at 50 W/(m·K) in the two US units:

1. In Btu/(h·ft·°F): multiply by 0.577789.

   50 × 0.577789 = 28.89 Btu/(h·ft·°F)

2. In Btu·in/(h·ft²·°F), the unit insulation data sheets use: multiply by 6.93347.

   50 × 6.93347 = 346.7 Btu·in/(h·ft²·°F)

Common conversions

The Btu and calorie values are the International Table (IT) units.

Thermal conductivity units

• Watt / meter / K (W/m/K): The thermal conductivity measured in watts per meter per Kelvin represents the amount of heat (in watts) that can be conducted through a one-meter thickness of a material for every one-degree temperature difference.
  Conversion Factor: 1 W/m/K (Base Unit)

• Watt / centimeter / °C (W/cm/°C): Similar to W/m/K, this unit measures thermal conductivity on a smaller scale, using centimeters. Because a temperature difference of 1 °C is equal to a temperature difference of 1 K, the unit W/cm/°C is equivalent to W/cm/K.
  Conversion Factor: 1 W/cm/°C = 100 W/m/K

• Kilowatt / meter / K (kW/m/K): This is the thermal conductivity expressed in kilowatts per meter per Kelvin.
  Conversion Factor: 1 kW/m/K = 1000 W/m/K

• Calorie / second / cm / °C (cal/s/cm/°C): In this unit, thermal conductivity is measured in calories per second per centimeter per degree Celsius.
  Conversion Factor: 1 cal(IT)/s/cm/°C = 418.68 W/m/K; 1 cal(th)/s/cm/°C = 418.4 W/m/K

• Kilocalorie / hour / meter / °C (kcal/h/m/°C): Expressed in kilocalories per hour per meter per degree Celsius, this unit provides a larger scale for thermal conductivity.
  Conversion Factor: 1 kcal(IT)/h/m/°C = 1.163 W/m/K; 1 kcal(th)/h/m/°C = 1.1622 W/m/K

• Btu foot / hour / foot² / °F (Btu•ft/h/°F): The British Thermal Unit per hour per square foot per degree Fahrenheit is a unit commonly used in the United States.
  Conversion Factor: 1 Btu(IT)•ft/h/°F = 1.7307 W/m/K; 1 Btu(th)•ft/h/°F = 1.7296 W/m/K

• Btu inch / hour / foot² / °F (Btu•in/h/°F): This unit represents thermal conductivity using inches instead of feet.
  Conversion Factor: 1 Btu(IT)•in/h/°F = 0.14423 W/m/K; 1 Btu(th)•in/h/°F = 0.14413 W/m/K

Frequently asked questions

Is W/(m·K) the same as W/(m²·K)?

No. W/(m·K) is a conductivity, a property of the material. W/(m²·K) is a heat transfer coefficient, or U-value, which belongs to a layer of a given thickness: U = k / thickness. Those are converted in the Heat Transfer Coefficient Converter.

How do you get an R-value from the thermal conductivity?

Divide the thickness by the conductivity: R = thickness / k. For example, 0.1 m of mineral wool at 0.04 W/(m·K) gives 0.1 / 0.04 = 2.5 m²·K/W.

Can thermal conductivity be converted to specific heat?

No, they are different properties. Conductivity is how fast heat moves through a material, and specific heat is how much heat it takes to warm it. They meet in the thermal diffusivity, α = k / (ρ * c), where ρ is the density and c the specific heat.