Thermal Resistance converter
How much a component's temperature rises per watt it has to shed, the junction-to-ambient figure on every heatsink datasheet.
Converter
Quick pairs
tap to loadOne kelvin per watt in every thermal resistance unit
5 rows| Unit | Symbol | 1 K/W equals |
|---|---|---|
| Degree Celsius per watt | °C/W | 1 |
| Kelvin per kilowatt | K/kW | 1,000 |
| Kelvin per milliwatt | K/mW | 0.001 |
| Degree Fahrenheit hour per BTU | °F·h/BTU | 0.5275279263 |
| Degree Fahrenheit second per BTU | °F·s/BTU | 1,899.100535 |
How the kelvin per watt to degree fahrenheit hour per btu conversion works
Thermal resistance measures how many degrees a component's temperature climbs for every watt of heat it must dissipate, and this converter uses kelvin per watt as the reference. Degree Celsius per watt is identical to kelvin per watt (factor 1) because both use the same size temperature step. Kelvin per kilowatt and kelvin per milliwatt are just metric-prefixed versions, scaled by 0.001 and 1000. The BTU-based units — degree Fahrenheit-hour per BTU and degree Fahrenheit-second per BTU — mix an imperial energy unit (BTU) with an imperial temperature step and a time unit, which is why their factors (about 1.896 and 0.000527) look less tidy.
The featured conversion is kelvin per watt to degree Fahrenheit-hour per BTU: °F·h/BTU = K/W × 0.5275279263. Reverse it by multiplying by 1.895634241.
A heatsink datasheet rated at 1.5 °C/W (the same numeric value as 1.5 K/W) converts to 1.5 × 0.5275279263 ≈ 0.791 °F·h/BTU. A beefier heatsink at 0.4 K/W converts to 0.4 × 0.5275279263 ≈ 0.211 °F·h/BTU — the lower the thermal resistance, the better the part sheds heat for a given temperature rise.
Thermal resistance is the core spec electronics engineers use to pick heatsinks and judge whether a CPU, power transistor, or LED driver will overheat: multiply the component's power dissipation by its junction-to-ambient resistance and add ambient temperature to predict the junction temperature. The same concept, in different units, governs HVAC component selection and some materials testing where imperial BTU-based figures are still standard in US engineering documentation.
A common point of confusion is treating electronics thermal resistance (K/W, a property of one specific component or assembly) as the same thing as a building insulation R-value, which is also sometimes called thermal resistance but is expressed per unit area (ft²·°F·h/BTU) rather than for a whole part. The two numbers aren't interchangeable, and plugging an insulation R-value into an electronics calculation — or vice versa — will give a nonsensical result because an area dimension is missing or extra.
Questions
How many degree Fahrenheit-hour per BTU equal one kelvin per watt?
One K/W equals 0.5275279263 °F·h/BTU. Both describe the same physical property: temperature rise per unit of heat flow, just on different unit systems.
Which units does this thermal resistance converter cover?
6 units referenced to kelvin per watt: kelvin per watt, degree Celsius per watt, kelvin per kilowatt, kelvin per milliwatt, degree Fahrenheit-hour per BTU, and degree Fahrenheit-second per BTU.
Does rounding matter much in thermal resistance conversions?
For component selection, yes — heatsink ratings are often compared to the second decimal place (e.g. 0.79 vs 0.85 °F·h/BTU), so it's worth keeping at least three significant figures through the conversion rather than rounding early.
When would I use kelvin per watt instead of degree Fahrenheit-hour per BTU?
K/W (or equivalently °C/W) is the standard unit on virtually all modern electronics and heatsink datasheets worldwide; the BTU-based unit mainly appears in older US imperial engineering documents or when cross-referencing legacy specs.
Is thermal resistance (K/W) the same as a building's R-value?
No — despite the shared name, R-value is thermal resistance per unit area (ft²·°F·h/BTU), used for insulation and building envelopes, while K/W here applies to a single component like a heatsink or transistor package with no area term involved.
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