Thermal Resistance Converter

Kelvin/Watt (K/W)

The SI unit of thermal resistance. It represents the temperature difference in kelvin required to produce a heat flow of one watt. R = ΔT / Q.

Common uses: International standards, scientific research, electronics cooling, thermal interface materials.

Degree Fahrenheit Hour/Btu (°F·h/Btu)

Thermal resistance using US customary units. Represents the temperature difference in Fahrenheit required to produce a heat flow of one BTU per hour. 1 K/W ≈ 0.5275 °F·h/Btu.

Common uses: US building insulation R-values, HVAC calculations, construction standards.

Degree Fahrenheit Second/Btu (°F·s/Btu)

Thermal resistance using time intervals of seconds instead of hours. 1 °F·h/Btu = 3600 °F·s/Btu.

Note: Less commonly used but appears in specialized thermal calculations.

What is Thermal Resistance?

Thermal resistance is a measure of how well a material resists heat flow. Higher thermal resistance means better insulation properties. The heat flow equation is: Q = ΔT / R

• Q: Heat flow rate (Watts)
• ΔT: Temperature difference (Kelvin or °C)
• R: Thermal resistance (K/W)

R-Value in Building Insulation

In construction, R-value (expressed in °F·ft²·h/Btu) is the thermal resistance of insulation materials. Higher R-values indicate better insulation.

• Fiberglass batts: R-3.2 to R-3.8 per inch
• Mineral wool: R-3.1 to R-3.8 per inch
• Rigid foam: R-5 to R-6.5 per inch
• Spray foam: R-5.5 to R-7 per inch
• Typical wall assembly: R-13 to R-21
• Typical attic: R-38 to R-60

Total Thermal Resistance (Series)

When multiple layers are stacked, total thermal resistance is the sum: R_total = R₁ + R₂ + R₃ + ...

Example: Drywall (R-0.56) + Fiberglass (R-13) + Air film (R-0.68) = R-14.24 total