Convert US R-Value to RSI (m²·K/W) (ft2 F h/BTU to m2 K/W)
1 US R-value (ft²·°F·h/BTU) = 0.1761101837 square metre kelvin per watt (m²·K/W). 1 m²·K/W = 5.678263341 ft²·°F·h/BTU. Example: 13 ft²·°F·h/BTU = 13 × 0.1761101837 = 2.289432388 m²·K/W.
Also searched as R-value to RSI, US R to m2K/W, imperial R value to metric and R to SI R-value.
1 ft²·°F·h/BTU = 0.1761101837 m²·K/W
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk R (US) to RSI converter to paste a column from Excel.
How to Convert US R-Value to RSI (m²·K/W)
- 1 ft²·°F·h/BTU = 0.1761101837 m²·K/W
- 1 m²·K/W = 5.678263341 ft²·°F·h/BTU
- Example: convert 13 ft²·°F·h/BTU to m²·K/W: 13 ft²·°F·h/BTU = 13 × 0.1761101837 m²·K/W = 2.289432388 m²·K/W
Formula
m²·K/W = ft²·°F·h/BTU × 0.1761101836823
or m²·K/W = ft²·°F·h/BTU ÷ 5.678263341113
Derivation from SI units:
- 1 ft²·°F·h/BTU_IT = 0.09290304 m² × (5/9) K × 3600 s ÷ 1055.05585262 J ≈ 0.17611 m²·K/W.
- Thermal resistance per unit area R = thickness ÷ conductivity, in m²·K/W; U = 1/ΣR.
Both units are defined exactly, so the factor is exact. US R-Value definition: US R-value; RSI (m²·K/W) definition: square metre kelvin per watt.
Worked examples
- A wall batt rated 13 ft²·°F·h/BTU is 2.289432388 m²·K/W.
13 ft²·°F·h/BTU × 0.1761101837 = 2.289432388 m²·K/W - Attic insulation rated 38 ft²·°F·h/BTU is 6.69218698 m²·K/W.
38 ft²·°F·h/BTU × 0.1761101837 = 6.69218698 m²·K/W
US R-Value to RSI (m²·K/W) conversion table
| US R-Value (ft²·°F·h/BTU) | RSI (m²·K/W) (m²·K/W) |
|---|---|
| 1 ft²·°F·h/BTU | 0.1761101837 m²·K/W |
| 3 ft²·°F·h/BTU | 0.528330551 m²·K/W |
| 5 ft²·°F·h/BTU | 0.8805509184 m²·K/W |
| 11 ft²·°F·h/BTU | 1.937212021 m²·K/W |
| 13 ft²·°F·h/BTU | 2.289432388 m²·K/W |
| 19 ft²·°F·h/BTU | 3.34609349 m²·K/W |
| 21 ft²·°F·h/BTU | 3.698313857 m²·K/W |
| 30 ft²·°F·h/BTU | 5.28330551 m²·K/W |
| 38 ft²·°F·h/BTU | 6.69218698 m²·K/W |
| 49 ft²·°F·h/BTU | 8.629399 m²·K/W |
Where it's used
US insulation R-values are converted to RSI (m²·K/W) for metric codes and U-value calculations. Multiply by 0.17611.
US R-Value to other thermal resistance (r-value) units
| Conversion | 1 ft²·°F·h/BTU equals |
|---|---|
| R (US) to RSI | 0.1761101837 m²·K/W |
| R (US) to clo | 1.136194733 clo |
| R (US) to tog | 1.761101837 tog |
| R (US) to square metre hour degree Celsius per kilocalorie | 0.2048161436 m²·h·°C/kcal |
Frequently asked questions
How do I convert US R-value to RSI?
Multiply by 0.17611: R-13 = 2.289432388 m²·K/W.
Why are US R-values larger numbers?
The US unit is about 5.7 times smaller than the SI unit, so the same insulation reads R-5.68 in the US for every RSI 1.
How many square metre kelvin per watt are in 1 US R-value?
1 ft²·°F·h/BTU = 0.1761101837 m²·K/W.
How do I convert US R-value to square metre kelvin per watt?
Multiply the value in ft²·°F·h/BTU by 0.1761101837, or divide it by 5.678263341. For example, 13 ft²·°F·h/BTU × 0.1761101837 = 2.289432388 m²·K/W.
Is the ft²·°F·h/BTU to m²·K/W conversion exact?
Yes. Both units are defined exactly, so the ratio is exact; its decimal form does not terminate and is shown here to 10 significant figures (more with the precision selector).
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "degree Fahrenheit hour square foot per British thermal unit_IT".
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Table 4 (derived units with special names).
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Convert US R-Value to RSI (m²·K/W) (ft2 F h/BTU to m2 K/W). Retrieved October 29, 2026, from https://scientificconverters.com/thermal-resistance/r-value-to-rsi/
IEEE
Scientific Converters, "Convert US R-Value to RSI (m²·K/W) (ft2 F h/BTU to m2 K/W)," scientificconverters.com. Accessed: Oct. 29, 2026. [Online]. Available: https://scientificconverters.com/thermal-resistance/r-value-to-rsi/