Heat Sink Temperature Calculator
When a component dissipates power, its temperature rises above the surrounding air by an amount set by how well heat can escape. This calculator uses the standard thermal resistance model to find that temperature. It takes the power dissipated in watts, the total thermal resistance of the path from the part out to the air in degrees Celsius per watt, and the ambient air temperature, then multiplies power by resistance to get the temperature rise and adds the ambient to get the final component temperature. The thermal resistance usually bundles the junction-to-case, case-to-sink and sink-to-air figures from the datasheet into one number. The model is the everyday tool for sizing a heatsink, checking that a regulator or transistor stays within its rated limit, or deciding whether forced airflow is needed. Enter your own power, thermal resistance and ambient values to design a thermal solution, sanity-check a vendor's numbers, or work out the worst-case temperature inside a sealed enclosure. Always use the hottest air the device will really see and leave headroom below the maximum the part allows. Every figure here is computed deterministically from the thermal resistance relationship, shown in full below, with a worked example that reconciles exactly to the calculator so you can follow each step.
Component temperature equals power times thermal resistance, plus ambient: T = P x Rth + Tambient. Dissipating 10 W through a 2.5 degC/W path at 25 degC ambient gives a component temperature of 50.00 degC.
Heat sink temperature formula
T = P x Rth + Tambient
P = power dissipated (W)
Rth = total thermal resistance (degC/W)
Tambient = surrounding air temperature (degC)
T = component temperature (degC)
The temperature rise above ambient is the power multiplied by the total thermal resistance; adding the ambient air temperature gives the component temperature.
Worked example
A device dissipates 10 W through a thermal path of 2.5 degrees Celsius per watt, in air at 25 degrees Celsius.
- Temperature rise = 10 x 2.5 = 25 degC
- Add ambient: 25 + 25 = 50
- Component temperature = 50.00 degC
The component sits at 50.00 degrees Celsius. These are the calculator's default inputs, so the result above matches the widget exactly.
Component temperature at 25 degC ambient
For a fixed 10 W dissipation, a lower thermal resistance keeps the part cooler.
| Rth (degC/W) | Rise (degC) | Temperature (degC) |
|---|---|---|
| 1.0 | 10.00 | 35.00 |
| 2.5 | 25.00 | 50.00 |
| 4.0 | 40.00 | 65.00 |
| 6.0 | 60.00 | 85.00 |
Ambient temperature and climate data: US National Oceanic and Atmospheric Administration (NOAA).
Heat sink temperature calculator: frequently asked questions
How does a heat sink set the temperature?
Heat flows from a hot component out to the surrounding air through a chain of thermal resistances. The temperature rise above ambient equals the power dissipated multiplied by the total thermal resistance in kelvin per watt. Adding that rise to the ambient air temperature gives the component temperature.
What is thermal resistance?
Thermal resistance, in degrees Celsius (or kelvin) per watt, measures how much a path resists heat flow. A higher value means a bigger temperature rise for the same power. The total figure usually combines the junction-to-case, case-to-sink and sink-to-air resistances; manufacturers list each in the datasheet.
How do I work out the component temperature?
Multiply the dissipated power by the total thermal resistance to get the temperature rise, then add the ambient temperature. For 10 watts, 2.5 degrees per watt and 25 degrees ambient, the rise is 25 degrees and the component sits at 50 degrees Celsius.
What ambient temperature should I use?
Use the worst-case air temperature the device will actually see, which inside an enclosure can be well above room temperature. Designing for a hot summer day or a sealed cabinet protects against overheating; using an optimistic 20 degrees can leave no margin.
How do I keep a part within its rated limit?
Compare the calculated temperature with the maximum the datasheet allows and leave headroom. If it runs too hot, lower the thermal resistance with a bigger heatsink or airflow, reduce the dissipated power, or improve the thermal interface between the part and the sink.
Official sources
- Ambient temperature and climate reference data: US National Oceanic and Atmospheric Administration (NOAA). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.