Thermal Resistance Calculator
thermal resistance calculator R-value, U-factor, and thermal resistance from thickness and thermal conductivity. Accurate engineering formulas and unit conversions for engineers, students & technicians.
Calculate Thermal Resistance Calculator
Enter your engineering parameters below to compute verified physical and mathematical metrics.
Calculation Results
Calculated using verified physical methodology: Absolute Thermal Resistance: R_{th} = \d / k \cdot A
Area R-Value: R_{val} = \d / k U\text{-Factor}: U = \1 / R_{val} = \k / d
Quick Summary
The Thermal Resistance Calculator determines absolute thermal resistance ({th} = d / (k \cdot A)$), SI R-value, US Imperial R-value, U-factor, and thermal conductance.
Formula Explanation
Absolute Thermal Resistance: R_{th} = \d / k \cdot A
Area R-Value: R_{val} = \d / k U\text{-Factor}: U = \1 / R_{val} = \k / d
How It Works
The Thermal Resistance Calculator determines absolute thermal resistance ({th}$ in K/W), area-specific SI R-value ({val} = d/k$ in m²·K/W), US Customary R-value ({\text{US}}$), and thermal transmittance ($-factor = /R_{val}$). It enables building envelope engineers and electronics cooling designers to optimize thermal insulation barriers.
Step-by-Step Worked Example
Practical Problem: Calculate thermal resistance, SI R-value, US R-value, and U-factor for a 50 mm (0.05 m) mineral wool insulation batt ( = 0.035\text{ W/m}\cdot\text{K}$) over 1.0 m² surface area.
- Step 1: Identify Input Parameters: Layer Thickness = 0.05\text{ m}$, Thermal Conductivity = 0.035\text{ W/m}\cdot\text{K}$, Area = 1.0\text{ m}^2$.
- Step 2: Calculate Absolute Thermal Resistance (R_th): {th} = \d / k \cdot A = \0.05 / 0.035 \times 1.0 = 1.4286\text{ K/W}$.
- Step 3: Calculate SI Area R-Value (R_val): {val} = \d / k = \0.05 / 0.035 = 1.4286\text{ m}^2\cdot\text{K/W}$.
- Step 4: Calculate Thermal Transmittance (U-Factor): = \1 / R_{val} = \1 / 1.4286 = 0.7000\text{ W/m}^2\cdot\text{K}$.
- Step 5: Convert to Imperial US R-Value: {\text{US}} = R_{val} \times 5.67826 = 1.4286 \times 5.67826 = \text{R-}8.11\text{ (ft}^2\cdot^\circ\text{F}\cdot\text{hr/BTU)}$.
Real-World Calculation Examples
Scenario 1: Residential Fiberglass Attic Insulation
Parameters: = 0.15\text{ m}$ (150 mm), = 0.040\text{ W/m}\cdot\text{K}$, = 1.0\text{ m}^2$
Result: {val} = 3.75\text{ m}^2\cdot\text{K/W}$ (US R-21.29), = 0.267\text{ W/m}^2\cdot\text{K}$. Standard roof thermal barrier.
Scenario 2: Rigid Polyisocyanurate Wall Board
Parameters: = 0.05\text{ m}$ (50 mm), = 0.022\text{ W/m}\cdot\text{K}$, = 1.0\text{ m}^2$
Result: {val} = 2.27\text{ m}^2\cdot\text{K/W}$ (US R-12.91), = 0.440\text{ W/m}^2\cdot\text{K}$. High-performance foam insulation.
Scenario 3: Solid Concrete Foundation Wall
Parameters: = 0.20\text{ m}$ (200 mm), = 1.300\text{ W/m}\cdot\text{K}$, = 1.0\text{ m}^2$
Result: {val} = 0.15\text{ m}^2\cdot\text{K/W}$ (US R-0.87), = 6.500\text{ W/m}^2\cdot\text{K}$. Uninsulated concrete thermal resistance.
Scenario 4: CPU Alumina Ceramic Substrate
Parameters: = 0.002\text{ m}$ (2 mm), = 25.000\text{ W/m}\cdot\text{K}$, = 0.001\text{ m}^2$
Result: {th} = 0.0800\text{ K/W}$, = 12,500\text{ W/m}^2\cdot\text{K}$. Electronics thermal interface resistance.
Key Benefits of Using This Calculator
Dual SI & US R-Value Conversion
Computes SI R-value (m²·K/W) and US Imperial R-value (ft²·°F·hr/BTU) simultaneously.
U-Factor Transmittance Output
Calculates building thermal transmittance U-factor ( = 1/R_{val}$) compliant with ASHRAE codes.
Building & Electronics Application
Suitable for both building wall insulation design and microelectronic heatsink thermal resistance analysis.
Instant Copy & Print Export
Export calculated thermal metrics directly into project reports with 1-click action buttons.
Frequently Asked Questions (FAQ)
What is thermal resistance?
Thermal resistance measures a material layer's opposition to heat flow, defined as temperature difference divided by heat rate (R_th = dT / Q_dot = d / k*A).
What is R-value?
R-value is the area-specific thermal resistance R_val = d / k. Higher R-values indicate greater thermal insulation performance.
What is the difference between SI R-value and US R-value?
1 SI R-value unit (m²·K/W) equals 5.67826 US R-value units (ft²·°F·hr/BTU). US R-19 = 3.35 m²·K/W.
What is U-factor (U-value)?
U-factor is thermal transmittance, the reciprocal of R-value (U = 1 / R_val = k / d). Lower U-factors mean better insulation.
How do multi-layer thermal resistances combine in series?
For multi-layer walls in series: R_total = R1 + R2 + R3 + ... + R_internal_air + R_external_air.
How calculate R-value from thickness and thermal conductivity?
R_val = thickness (meters) / thermal conductivity (W/m·K).
What is thermal conductance (G_th)?
Thermal conductance G_th = 1 / R_th = (k * A) / d is the reciprocal of absolute thermal resistance (measured in W/K).
Why is R-value important in building energy codes?
Building energy codes (IECC, ASHRAE 90.1) mandate minimum wall/attic R-values to minimize heating and cooling HVAC energy consumption.
Does doubling insulation thickness double the R-value?
Yes, R-value scales linearly with material thickness d (e.g. 100 mm insulation has twice the R-value of 50 mm insulation of the same material).
What is thermal interface resistance in electronics?
In microelectronics, junction-to-case thermal resistance R_th (K/W) determines CPU chip temperature rise per Watt of electrical power dissipated.