Thermal Conductivity Conversion Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/10/2026
To convert a thermal conductivity, it is reduced to watts per meter-kelvin (W/(m·K)), then converted into the target unit. A conductivity of 1 W/(m·K) equals about 6.933 BTU·inch per hour-square foot-°F.
Explanation
Thermal conductivity, denoted λ (lambda), measures a material's intrinsic ability to conduct heat: the lower λ is, the better the insulator. This is exactly the value used by our required insulation thickness calculator and our insulation thermal resistance calculator to determine, from a given material, the thickness needed to reach a target insulating performance. The watt per meter-kelvin (W/(m·K)) is the SI unit, the one shown on most European technical datasheets for insulation materials (fiberglass wool around 0.032 to 0.040 W/(m·K), expanded polystyrene around 0.030 to 0.038 W/(m·K)). The BTU·inch per hour-square foot-degree Fahrenheit (BTU·in/(h·ft²·°F)) remains the reference unit in the United States for the same datasheets; the kilocalorie per hour-meter-degree Celsius (kcal/(h·m·°C)), finally, is still found in some older technical documents or in countries that kept this convention. Be careful not to confuse λ with thermal resistance (R, in m²·K/W, the very quantity computed by our insulation thermal resistance calculator): resistance depends on both the material AND its thickness (R = thickness ÷ λ), while conductivity is a property of the material alone, independent of how much of it is used.
Example: converting 1 W/(m·K) to BTU·in/(h·ft²·°F)
Inputs
Value: 1. Starting unit: W/(m·K). Target unit: BTU·in/(h·ft²·°F).
Calculation
1 W/(m·K) ÷ 0.144228 ≈ 6.933444 BTU·in/(h·ft²·°F).
Result
1 W/(m·K) equals about 6.933 BTU·in/(h·ft²·°F).
Frequently asked questions
Where do the conversion factors used here come from?
These factors follow directly from the exact physical definitions of the base units involved (the foot, the inch, the hour, the Fahrenheit degree gap in kelvins, the BTU, and the thermochemical calorie), the same values already used by our energy conversion calculator. They are therefore not measured approximations but exact relationships, independently recalculated by dimensional analysis before publication.
Why is a low thermal conductivity sought for an insulator?
Because thermal conductivity measures how easily heat passes through a material: the lower λ is, the less heat passes through a given thickness, and the better the material's insulating power. This is why high-performance insulation materials (fiberglass, mineral wool, polystyrene) all show very low λ values, generally below 0.04 W/(m·K).
What is the difference between conductivity and thermal resistance?
Conductivity (λ) is a property of the material alone, independent of its thickness — two plates of the same material, one thin and one thick, have exactly the same conductivity. Thermal resistance (R), on the other hand, depends on both the material and its thickness (R = thickness ÷ λ): the thick plate offers a higher thermal resistance, so better insulation in practice, despite an identical conductivity.