US R-Value (ft²·°F·h/BTU)
The US R-value, in ft²·°F·h/BTU, is the number printed on US insulation: R-13 for a 2×4 wall, R-38 to R-49 for attics. One US R unit is 0.17611 m²·K/W, so R-13 ≈ RSI 2.29.
Symbol: ft²·°F·h/BTU (ASCII: ft2 F h/BTU)
Quantity: thermal resistance per unit area (insulation R-value)
SI relation: 1 ft²·°F·h/BTU = 0.1761101836823 m²·K/W (exact)
Derivation: 1 ft²·°F·h/BTU_IT = 0.09290304 m² × (5/9) K × 3600 s ÷ 1055.05585262 J ≈ 0.17611 m²·K/W.
Exact: yes, by definition
Typical uses
- US insulation labels (R-13, R-19, R-38)
- IECC and ASHRAE 90.1 envelope requirements
- Comparing US and metric insulation
Convert US R-value to other units
| Conversion | 1 ft²·°F·h/BTU equals | Reverse |
|---|---|---|
| R (US) to RSI | 0.1761101837 m²·K/W | RSI to R (US) |
| R (US) to clo | 1.136194733 clo | clo to R (US) |
| R (US) to tog | 1.761101837 tog | tog to R (US) |
| R (US) to square metre hour degree Celsius per kilocalorie | 0.2048161436 m²·h·°C/kcal | square metre hour degree Celsius per kilocalorie to R (US) |
Open the R-Value Converter (US R to RSI, m²·K/W) to convert any value between all units.
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".
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). US R-Value (ft²·°F·h/BTU). Retrieved October 29, 2026, from https://scientificconverters.com/units/square-foot-hour-fahrenheit-per-btu/
IEEE
Scientific Converters, "US R-Value (ft²·°F·h/BTU)," scientificconverters.com. Accessed: Oct. 29, 2026. [Online]. Available: https://scientificconverters.com/units/square-foot-hour-fahrenheit-per-btu/