Convert thermal resistance between kelvin/watt, °C/W and °F·h/BTU.
Heat • 5 units
All 5 units on the Thermal Resistance Converter are defined against the Kelvin/Watt (K/W), so each result is one conversion factor away from a single reference rather than the end of a chain of roundings.
The conversion this page is most often opened for is ready before you type anything: 1 K/W = 0.527527993 °F·h/BTU. Change either side and every row in the table recalculates with it.
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The imperial row inverts more awkwardly than most: 1 K/W is 0.5275 °F·h/BTU, and 1 °F·h/BTU is 1.8956 K/W. The kelvin and Celsius rows, by contrast, are identical, because both are temperature intervals rather than absolute readings. That identity is why datasheets use K/W and °C/W interchangeably without anyone objecting.
The quantity is most useful worked backwards from a temperature limit. A device with a maximum junction temperature of 125 °C sitting in a 40 °C ambient has an 85 K budget to spend; at 10 W of dissipation the entire path from junction to air must therefore come in under 8.5 K/W. Every element in that path — the die attach, the case, the interface material, the heatsink — spends part of the budget, and the sum is what decides whether the design survives, which is why thermal resistances are quoted for each stage separately.
The most common mistake in this area is converting a building R-value with these factors. Construction R-values are area-normalised, in ft²·°F·h/BTU or m²·K/W, so they are a different quantity from the absolute thermal resistance this page handles and no factor here applies to them. An R-13 batt in US units corresponds to about 2.29 m²·K/W, a conversion that needs the area-based factor of 0.1761. Passing it through the absolute-resistance conversion instead yields a number with no physical meaning and no obvious sign that anything went wrong.
Quick reference — 1 Kelvin/Watt (K/W) is equal to:
| Degree °C/Watt | °C/W | 1 |
| Kelvin/Kilowatt | K/kW | 1,000 |
| Kelvin/Milliwatt | K/mW | 0.001 |
| °F·hour/BTU | °F·h/BTU | 0.527527993 |
5 units of thermal resistance, each a fixed multiple of the K/W. The table spans 1,000,000:1, from K/kW (0.001 K/W) to K/mW (1000 K/W). Conversion is one multiplication into the base unit and one division out of it, with no lookup table and no approximation.
value_to = value_from × (factor_from ÷ factor_to)1 K/W = 1 K/W1 °C/W = 1 K/W1 K/kW = 0.001 K/W1 K/mW = 1000 K/W1 °F·h/BTU = 1.89563 K/Wwhere:
Assumptions: Factors are exact definitions. Full double precision is carried internally and rounding is applied only for display.
Result25 K/W = 13.1882 °F·h/BTU
Thermal resistance, in kelvins per watt (K/W), states how much temperature rise a component suffers per watt it must dissipate. The analogy to electrical resistance is exact: temperature difference plays the role of voltage, heat flow the role of current, and resistances in a path simply add.
That additivity is what makes heatsink selection arithmetic rather than guesswork. A transistor with a junction-to-case resistance of 1 K/W, an insulating pad at 0.5 K/W and a heatsink at 2 K/W totals 3.5 K/W, so 20 W of dissipation implies a 70 K rise above ambient. Datasheets mix K/W, °C/W — numerically identical, since these are intervals — and the imperial °F·h/BTU used in building insulation.