Thermal Resistance Converter
ScienceConvert thermal resistance between Kelvin per watt, Celsius per watt, and Fahrenheit-hour per BTU — used for electronics cooling and insulation design.
From
To
All conversionsfor 1 Kelvin per Watt (K/W)
| Kelvin per Watt (K/W) | 1 |
| Celsius per Watt (°C/W) | 1 |
| Fahrenheit-Hour per BTU (°F·h/BTU) | 0.52753746 |
What is a Thermal Resistance?
The Thermal Resistance Converter converts thermal resistance between Kelvin per watt, Celsius per watt, and the imperial Fahrenheit-hour per BTU. Thermal resistance measures how much temperature difference builds up across a component or material for a given rate of heat flow — a key specification in electronics cooling (chip junction-to-ambient resistance) and building insulation design.
Enter a value in any supported unit and the converter calculates the equivalent instantly. For related thermal quantities, see the Thermal Conductivity Converter and Heat Transfer Coefficient Converter.
How to use this Thermal Resistance calculator
- Choose your starting unit from the source dropdown — for example, "Kelvin per Watt (K/W)".
- Enter the numeric value you want to convert in the input field.
- Choose your target unit from the destination dropdown — for example, "Fahrenheit-Hour per BTU (°F·h/BTU)".
- Read the converted result, which updates instantly as you type or change units.
- Use the swap (⇅) button if you need to reverse the conversion direction.
- Use the copy button to grab the result for a thermal design calculation or datasheet comparison.
Formula & Methodology
The converter's base unit is Kelvin per watt (K/W). Every supported unit has a fixed multiplier: - 1 Celsius per watt (°C/W) = 1 K/W (identical degree size) - 1 Fahrenheit-hour per BTU (°F·h/BTU) ≈ 1.8956 K/W Any conversion follows: Result = Input × (toBase of source unit ÷ toBase of target unit) Worked example — converting a heatsink rated at 5 K/W to °F·h/BTU: Result = 5 × (1 ÷ 1.8956) = 2.638 °F·h/BTU This is the equivalent rating you'd see on a datasheet using the imperial thermal resistance convention.
Frequently Asked Questions
Thermal resistance measures how much a material or component resists the flow of heat, expressed as the temperature difference produced per unit of heat flow (power) — a higher thermal resistance means a bigger temperature difference builds up for the same amount of heat trying to pass through.
A chip's datasheet specifies junction-to-case or junction-to-ambient thermal resistance (often in °C/W), which tells engineers how much the chip's internal temperature will rise above ambient for a given power dissipation — critical for confirming a heatsink or cooling solution keeps the chip within its safe operating temperature.
No conversion is needed for the value itself — °C/W and K/W are numerically identical, since a Celsius degree interval and a Kelvin interval are the same size. Only the unit label differs.
Multiply the °F·h/BTU value by 1.8956, the combined factor accounting for the different temperature interval size (°F vs K) and the different power/energy units (BTU/hour vs watts). Enter your value with 'Fahrenheit-Hour per BTU (°F·h/BTU)' as the source and 'Kelvin per Watt (K/W)' as the target to apply this automatically.
Consumer electronics heatsinks commonly range from around 1 to 20 K/W depending on size and airflow — smaller, passively cooled heatsinks have higher (worse) thermal resistance, while larger heatsinks with active airflow have lower (better) thermal resistance.
For cooling applications, yes — lower thermal resistance means less temperature rise for a given heat load, which is desirable for keeping components cool. For insulation applications, the goal is the opposite (higher resistance to heat flow), which is why insulation is typically rated using R-value rather than raw thermal resistance.
Thermal conductivity is a material property (how well a material conducts heat per unit thickness and area), while thermal resistance is a property of a specific component or path (accounting for its actual thickness, area, and material) — thermal resistance is what you calculate from thermal conductivity once you know the specific geometry involved. See the [Thermal Conductivity Converter](/thermal-conductivity-converter/) for the material-property side.
Yes — thermal resistances in series (like a chip junction, through its case, through a heatsink, to ambient air) add together the same way series electrical resistances do, which is why datasheets often break down thermal resistance into junction-to-case and case-to-ambient components that sum to a total.
Thermal resistance (K/W) describes a specific component or path's total resistance to heat flow, while heat transfer coefficient (W/m²·K) describes a surface's heat transfer rate per unit area — heat transfer coefficient is more useful for comparing materials or surfaces independent of size, while thermal resistance applies to a specific real component. See the [Heat Transfer Coefficient Converter](/heat-transfer-coefficient-converter/) for that related quantity.
Add up the thermal resistance of each stage in series — junction-to-case, case-to-heatsink (interface material), and heatsink-to-ambient — after converting all values to the same unit, giving a total that predicts the chip's temperature rise above ambient for a given power dissipation.
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