Thermal Resistance Calculator — Heat Transfer Resistance Converter
Convert between thermal resistance units including K/W, °C/W, R-value, and more. Essential for heat transfer analysis, insulation design, and thermal management. See also our Thermal Conductivity Calculator and Specific Heat Calculator.
How to Convert Thermal Resistance
- Enter the thermal resistance value to convert.
- Select the source unit from the dropdown.
- Click Calculate to see the value in all other units.
- Higher thermal resistance means better insulation.
Thermal Resistance Formula
R = ΔT / Q
Where:
R = Thermal resistance (K/W or °C/W)
ΔT = Temperature difference (K or °C)
Q = Heat flow rate (W)
For conduction through a material:
R = L / (k × A)
Where: L = thickness (m), k = thermal conductivity (W/m·K), A = area (m²)
For convection:
R = 1 / (h × A)
Where: h = heat transfer coefficient (W/m²·K), A = area (m²)
R-value (insulation rating):
R-value = thickness / thermal conductivityExample Calculation
Problem: A wall has thermal resistance of 0.1 K/W. What is its R-value?
Given: R = 0.1 K/W
Solution: R-value = 0.1 × (1/0.176110) = 0.568 °F·h·ft²/Btu
Answer: The R-value is approximately 0.57.
Common Thermal Resistance Values
| Material/Application | Thermal Resistance | R-value |
|---|---|---|
| Air gap (20mm) | 0.18 K·m²/W | R-1.0 |
| Fiberglass insulation (3.5") | 2.3 K·m²/W | R-13 |
| Foam board (1") | 1.4 K·m²/W | R-8 |
| Double-pane window | 0.35 K·m²/W | R-2 |
| Brick wall (4") | 0.072 K·m²/W | R-0.4 |
| Concrete block (8") | 0.14 K·m²/W | R-0.8 |
| Wood siding (0.5") | 0.11 K·m²/W | R-0.6 |
| Drywall (0.5") | 0.079 K·m²/W | R-0.45 |
Technical Details
Thermal resistance quantifies a material's ability to resist heat flow. It's the reciprocal of thermal conductance and is additive for layers in series. Higher thermal resistance indicates better insulation properties. The R-value is commonly used in building construction to rate insulation effectiveness. Thermal resistance depends on material properties, thickness, and geometry. For composite walls, total resistance equals the sum of individual layer resistances plus contact resistances. Temperature differences in Kelvin and Celsius are equivalent for thermal resistance calculations.
Frequently Asked Questions
What is thermal resistance?
Thermal resistance measures how well a material resists heat flow. It's the temperature difference divided by heat flow rate. Higher values indicate better insulation.
How is R-value related to thermal resistance?
R-value is thermal resistance per unit area, commonly used in construction. It equals thickness divided by thermal conductivity, expressed in °F·h·ft²/Btu or K·m²/W.
Can thermal resistances be added?
Yes, for layers in series (like wall components), thermal resistances add directly. For parallel paths, use the reciprocal formula: 1/R_total = 1/R₁ + 1/R₂ + ...
What affects thermal resistance?
Material properties (thermal conductivity), thickness, area, temperature, moisture content, and air gaps all affect thermal resistance. Insulation performance decreases with moisture and compression.
Why is thermal resistance important?
Thermal resistance determines energy efficiency in buildings, electronics cooling, and industrial processes. Higher resistance reduces heat loss, saving energy and improving comfort.