What is thermal resistance?

Thermal resistance measures how much a component or path resists the flow of heat, expressed as the temperature rise produced per watt of power dissipated. It's the thermal equivalent of electrical resistance, with power playing the role of current.

Why are K/W and °C/W numerically the same?

Thermal resistance describes a temperature difference, not an absolute temperature, and a 1 kelvin interval is exactly the same size as a 1 degree Celsius interval. So a value in K/W and the same value in °C/W describe the identical physical thermal resistance.

How do I convert °C/W to °F/W?

Multiply the °C/W value by 1.8. For example, 5 °C/W equals 9 °F/W, because a Fahrenheit degree interval is 5/9 the size of a Celsius or Kelvin interval.

What's the difference between thermal resistance (K/W) and R-value (m²·K/W)?

This converter covers thermal resistance in K/W, used for individual components like chips and heatsinks. R-value, measured in m²·K/W or ft²·°F·h/Btu, is normalized per unit area and used for insulation materials in construction. The two describe related but different things and aren't directly interchangeable.

How do I calculate temperature rise from power and thermal resistance?

Multiply the power dissipated in watts by the thermal resistance in K/W (or °C/W) to get the temperature rise above ambient. For example, 5 W through a 10 °C/W thermal resistance produces a 50°C rise.

What is a typical thermal resistance for a CPU heatsink?

Consumer CPU heatsinks typically range from about 0.1 to 1 °C/W depending on size and fan speed, while small component heatsinks for things like voltage regulators are often in the 10 to 50 °C/W range.

Why does a smaller thermal resistance mean better cooling?

A smaller thermal resistance produces a smaller temperature rise for the same amount of dissipated power, so lower values indicate a more effective path for heat to escape.

Is junction-to-ambient the same as junction-to-case thermal resistance?

No. Junction-to-case (often written RθJC) covers only the path from the chip's silicon to its package surface, while junction-to-ambient (RθJA) includes the case, any heatsink, and the surrounding air, so RθJA is almost always the larger number.

Is this calculator accurate enough for engineering use?

The conversion factors and formula are standard physics, so the math itself is reliable. Real thermal resistance figures depend heavily on airflow, mounting and ambient conditions, so always use manufacturer datasheet values for actual design work.

Is this thermal resistance converter free to use?

Yes, it is completely free, requires no registration, and runs entirely in your browser with no usage limits.

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Thermal Resistance Conversions

8 units · temperature rise calculator

Thermal Resistance Converter

Convert instantly between K/W, °C/W, °F/W and Btu-based thermal resistance units, then calculate temperature rise directly from power dissipation — all calculated in your browser.

8Thermal resistance units

1.8°F/W in 1 °C/W

0msServer round-trips

From

°C/W

To

°F/W

1.8°F/W

°F/W = °C/W × 1.8

Power dissipated

Power unit

Thermal resistance

Resistance unit

Ambient temperature

Ambient unit

50 °C rise

ΔT = P × Rθ = 5 W × 10 °C/W = 50°C rise (75°C final)

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Thermal resistance concepts & formulas

The math behind every conversion above, and the details that trip people up most.

Quick conversion table

Common values for your selected units in the converter above, updated automatically.

°C per Watt	°F per Watt

Thermal resistance unit reference

What each unit means, its exact size in K/W, and where you'll typically see it used.

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Frequently asked questions

Straight answers to the questions people ask most about thermal resistance and heat dissipation.

All calculations and conversions run locally in your browser using standard NIST/BIPM conversion factors. No data is sent anywhere.

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