Thermal Conductivity Converter: W/(m·K), Btu/(ft·h·°F) & More
Convert thermal conductivity (k or λ)—heat flow per area per temperature gradient—between SI, CGS, and imperial.
Convert thermal conductivity between W/(m·K), Btu/(ft·h·°F), cal/(cm·s·°C), and 14 units. Essential for heat transfer, insulation selection, and material datasheets. Free and instant.
What is thermal conductivity?
Thermal conductivity k (or λ) is the rate of heat flow per unit area per unit temperature gradient. Good conductors (metals) have high k; insulators (foams, still air) have low k. SI unit is W/(m·K): watts per meter of thickness per kelvin of temperature difference. Fourier’s law relates heat flux to the gradient:
So k is the constant that ties heat flux (W/m²) to the temperature gradient (K/m). US and imperial specs often use Btu·in/(ft²·h·°F) or Btu·ft/(ft²·h·°F); this converter includes those plus calorie-based CGS units so you can match any datasheet.
Key units explained
W/(m·K)
Factor: 1 (SI base)
Standard unit. Typical values: copper ~400, steel ~50, still air ~0.025 W/(m·K).
Btu·ft/(ft²·h·°F)
Factor: 1 ≈ 1.731 W/(m·K)
Common US form: Btu (IT) foot per hour per sq foot per °F. Often written Btu/(ft·h·°F).
cal/(cm·s·°C)
Factor: 1 ≈ 418.68 W/(m·K)
CGS unit. Still used in some chemistry and older references. 1 cal/(cm·s·°C) ≈ 418 W/(m·K).
Who uses this converter?
Mechanical and HVAC engineers move between W/(m·K) and Btu/(ft·h·°F) for insulation and heat exchanger specs. Materials engineers compare datasheets in SI and imperial. Building and construction often see Btu·in/(ft²·h·°F) for insulation. Students need to unify units for heat transfer calculations. All conversions run in your browser.
Common conversions at a glance
| From | To | Formula |
|---|---|---|
| Btu/(ft·h·°F) | W/(m·K) | × 1.731 |
| cal/(cm·s·°C) | W/(m·K) | × 418.68 |
| kW/(m·K) | W/(m·K) | × 1000 |
Thermal Conductivity FAQ
? How do I convert Btu/(ft·h·°F) to W/(m·K)?
Multiply by about 1.731. So 1 Btu (IT)/(ft·h·°F) ≈ 1.731 W/(m·K). The exact factor comes from 1 Btu ≈ 1055 J, 1 ft = 0.3048 m, 1 h = 3600 s, and 1 °F = 5/9 K. Use the converter above for inch-based and other variants.
? What is the relationship between thermal conductivity and R-value?
For a layer of thickness L and conductivity k, thermal resistance R = L/k (in K/W). So R-value (in °F·ft²·h/Btu or equivalent) is proportional to thickness and inversely proportional to k. Use our Thermal Resistance converter to switch R to K/W.
? How do I convert W/(m·K) to Btu/(ft·h·°F)?
Divide W/(m·K) by about 1.731. So 1 W/(m·K) ≈ 0.578 Btu (IT)/(ft·h·°F). Use the converter for Btu/(in·h·°F), kcal/(m·h·°C), and all 14 supported units. Common when switching between SI material data and US HVAC or building specs.
? What is Fourier’s law of heat conduction?
Heat flux q (W/m²) = −k × (temperature gradient). k is thermal conductivity in W/(m·K). So higher k means more heat flows for the same gradient. This converter lets you express k in Btu/(ft·h·°F), cal/(cm·s·°C), or 12 other units for textbooks and datasheets.
? What is a typical thermal conductivity for insulation vs metal?
Insulation (fiberglass, foam) is often 0.03–0.04 W/(m·K). Steel is about 50; copper ~400 W/(m·K). Use this converter when your table is in Btu/(ft·h·°F) and your model uses W/(m·K), or for kcal/(m·h·°C) and other metric variants.
? How do I convert thermal conductivity from Btu/(in·h·°F) to W/(m·K)?
Multiply by about 20.78. So 1 Btu/(in·h·°F) ≈ 20.78 W/(m·K). Inch-based units appear in some US datasheets. The converter supports both per-ft and per-in Btu units plus metric options so you can match any source.