Conversion method
Thermal resistance is temperature difference per heat-flow rate. Area-normalized insulation R-values are a different quantity.
°F·h/BTU IT = x × 0.52752792631
10 K/W = 5.275279 °F·h/BTU IT.
| K/W | °F·h/BTU IT |
|---|---|
| 1 | 0.527528 |
| 5 | 2.63764 |
| 10 | 5.275279 |
| 25 | 13.188198 |
| 50 | 26.376396 |
| 100 | 52.752793 |
Unit definitions and sources
Thermal resistance is temperature difference per heat-flow rate. Area-normalized insulation R-values are a different quantity.
| Unit and system | Use | Definition | Relationship |
|---|---|---|---|
| Kelvin per watt (K/W); si | Common units | Kelvin per watt: base (k-w) = value × 1. Common use: Thermal Resistance. Source checked 2026-09-20 (implementation review). | Exact definition; numerical display may be rounded |
| Fahrenheit hour per BTU (IT) (°F·h/BTU IT); si | Common units | Fahrenheit hour per BTU (IT): base (k-w) = value × 1.8956342406266344. Common use: Thermal Resistance. Source checked 2026-09-20 (implementation review). | Exact definition; numerical display may be rounded |
| Celsius interval per watt (°C/W); si | Specialist units | Celsius interval per watt: base (k-w) = value × 1. Common use: Thermal Resistance. Source checked 2026-09-20 (implementation review). | Exact definition; numerical display may be rounded |
| Kelvin per kilowatt (K/kW); si | Specialist units | Kelvin per kilowatt: base (k-w) = value × 0.001. Common use: Thermal Resistance. Source checked 2026-09-20 (implementation review). | Exact definition; numerical display may be rounded |
| Degree Fahrenheit hour/Btu (IT) (Δ°F·h/(BTU IT)); other | Specialist units | degree Fahrenheit hour/Btu (IT) = 1.8956342406266344 k-w, derived from the component SI/customary definitions. Common use: Thermal Resistance. Source checked 2026-09-20 (implementation review). | Exact definition; numerical display may be rounded |
| Degree Fahrenheit hour/Btu (th) (Δ°F·h/(BTU th)); other | Specialist units | degree Fahrenheit hour/Btu (th) = 1.896902829506595 k-w, derived from the component SI/customary definitions. Common use: Thermal Resistance. Source checked 2026-09-20 (implementation review). | Exact definition; numerical display may be rounded |
| Degree Fahrenheit second/Btu (IT) (Δ°F·s/(BTU IT)); other | Specialist units | degree Fahrenheit second/Btu (IT) = 0.0005265650668407318 k-w, derived from the component SI/customary definitions. Common use: Thermal Resistance. Source checked 2026-09-20 (implementation review). | Exact definition; numerical display may be rounded |
| Degree Fahrenheit second/Btu (th) (Δ°F·s/(BTU th)); other | Specialist units | degree Fahrenheit second/Btu (th) = 0.0005269174526407208 k-w, derived from the component SI/customary definitions. Common use: Thermal Resistance. Source checked 2026-09-20 (implementation review). | Exact definition; numerical display may be rounded |
Sources: NIST: SP 811 Appendix B.8: conversion factors; BIPM: SI prefixes
Precision of thermal resistance conversions
All 8 thermal resistance units convert through Kelvin per watt (K/W). 8 have an exact defined relationship to the base unit and 0 are conventional or measured values. Results and the tables on this page come from the same engine, so a table value can be checked against the converter directly.
Standard display shows up to six decimal places, switching to scientific notation for very large or small values. Calculation uses JavaScript binary floating point independently of display rounding, so extra digits are not a claim about measurement accuracy. Each unit lists its own source; a citation records where the definition comes from, not an independent review. See Conversion methodology for the review and correction process.