Thermal Resistance & Insulation R-Value Converter

Building Science, Architectural Thermodynamics & Thermal Resistance Metrology

Thermal resistance (R) quantifies a material's opposition to conductive heat transfer:

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• Universal R-Value Conversion Formulas (ASHRAE Standards)**:

US R-Value = Metric RSI × 5.678263

Metric RSI = US R-Value × 0.176110 = US R-Value5.678263

1 Tog = 0.10 m^2·K/W = 0.5678 US R | 1 Clo = 0.155 m^2·K/W = 0.8803 US R

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• U-Factor & Steady-State Heat Loss Equations**:

U_Metric = (1) / (RSI) ) | U_Imperial = (1) / (US R) )

Q = U × A × Δ T = (A × Δ T) / (R_SI) (Watts, W)

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• Standard Insulation & Assembly Benchmarks**:

• Standard 2x4 Wall (US R-13): RSI 2.289 m^2·K/W U = 0.437 W/(m^2·K) 874 W per 100m^2 @ 20^ Δ T

• 2x6 High-Efficiency Wall (US R-20): RSI 3.522 m^2·K/W U = 0.284 W/(m^2·K) 568 W

• Attic Ceiling (US R-49): RSI 8.629 m^2·K/W U = 0.116 W/(m^2·K)

• Double-Pane Low-E Window (US R-3.3): RSI 0.587 m^2·K/W U = 1.703 W/(m^2·K)

How to Use This Calculator

Enter your Thermal Resistance Magnitude (R-Value / RSI) (e.g. 13 in R), From Thermal Resistance Unit — choose from US R-Value (ft²·°F·h/BTU - US Insulation Standard), Metric RSI (m²·K/W - International / SI Standard), Absolute Resistance (K/W = °C/W - Electronics Heatsinks), To Thermal Resistance Unit — choose from Metric RSI (m²·K/W), US R-Value (ft²·°F·h/BTU), Tog Rating, Wall / Roof Surface Area (m²) (e.g. 100 in m²), Indoor-to-Outdoor Temp Difference (ΔT in °C) (e.g. 20 in Δ°C), and Building Envelope & Electronics Benchmark — choose from Custom Thermal Resistance, Standard 2x4 Wall Fiberglass Batt (US R-13) → RSI 2.289 m²·K/W | U = 0.437 W/(m²·K) | Q̇ = 874 W, High-Efficiency 2x6 Wall (US R-20) → RSI 3.522 m²·K/W | U = 0.284 W/(m²·K) | Q̇ = 568 W. Results update instantly as you type — adjust any value to compare scenarios.

The Formula

For electronics: RSI = R_abs * Area

Worked Example

A building architect specifying US R-13 fiberglass batt insulation converts the rating to Metric RSI 2.29 m²·K/W), calculating that a 100 m² wall facing a 20°C winter freeze loses 873.7 Watts of thermal energy.

Understanding Your Result

Unit conversions are exact by definition within a given measurement system (e.g., 1 km = exactly 1,000 m). Cross-system conversions (metric to imperial) use defined exchange factors: 1 inch = exactly 2.54 cm; 1 pound = 0.45359237 kg. Round your converted result to match the precision of your original measurement — expressing more decimal places than your input justifies implies false accuracy. For regulatory, legal, or safety-critical applications, verify which measurement system is required by the applicable standard.