What this converter does
This converter turns thermal conductivity between W/m·K, the US BTU·in/hr·ft²·°F (the “per-inch” form used for insulation), BTU/hr·ft·°F and mW/m·K — instantly and with exact factors. Type a value, pick the units, and read the answer as you type.
The per-inch BTU form is the one behind insulation R-values; the per-foot form is used for bulk materials. For temperature scales, see the Celsius to Fahrenheit converter.
The units it covers
Every unit is thermal conductivity, so each converts through the W/m·K with a fixed ratio.
View all units & their values
| Unit | Symbol | Value | Mainly used |
|---|---|---|---|
| Watt per m·K | W/m·K | 1 | SI unit — materials data |
| BTU·in per hr·ft²·°F | BTU·in/hr·ft²·°F | 0.14423 | US insulation (per inch) |
| BTU per hr·ft·°F | BTU/hr·ft·°F | 1.73073 | US bulk materials (per foot) |
| Milliwatt per m·K | mW/m·K | 0.001 | Gases, insulation, low k |
The formula
Each unit has a fixed value in W/m·K, so any conversion goes through it once:
result = value × factor_from ÷ factor_toWhere:
- value = the number you typed, in the “from” unit
- factor_from = the “from” unit’s value in W/m·K
- factor_to = the “to” unit’s value in W/m·K
Worked example
Convert 1 W/m·K to BTU·in/hr·ft²·°F.
1 BTU·in/hr·ft²·°F = 0.14423 W/m·K1 ÷ 0.14423 = 6.933 BTU·in/hr·ft²·°FSo 1 W/m·K is about 6.93 BTU·in/hr·ft²·°F.
The units in this example
The SI unit of thermal conductivity — heat flow per metre thickness per kelvin. Copper is ~400, water ~0.6, and still air ~0.026.
- 1 W/m·K ≈ 6.933 BTU·in/hr·ft²·°F
- 1 W/m·K ≈ 0.5778 BTU/hr·ft·°F
- 1 W/m·K = 1,000 mW/m·K
- copper ≈ 400 W/m·K
The US per-inch conductivity unit behind insulation R-values. It measures heat through a one-inch thickness over a square foot.
- 1 unit = 0.14423 W/m·K
- 6.933 units ≈ 1 W/m·K
- fiberglass ≈ 0.25 units
- 1 unit ≈ 0.0833 BTU/hr·ft·°F