Your Heat Sink & Thermal Resistance Calculator
Calculate the thermal resistance a heat sink must have for a given power, ambient and junction limit, estimate an extruded finned heat sink (fin efficiency.
- Free to use
- No signup
- Nothing to install
- Runs in your browser
Illustration. Open the tool for the real thing.
See it in action
The Heat Sink & Thermal Resistance Calculator with sample data entered and the result showing.
What is the Heat Sink & Thermal Resistance Calculator?
A heat sink is described by one number — its thermal resistance to ambient in K/W — and sizing one starts from the thermal 'Ohm's law': T_junction = T_ambient + P × (Rθjc + Rθcs + Rθsa). Enter the power to dissipate, the ambient temperature, the maximum junction temperature and the datasheet junction-to-case resistance and the interface (paste or pad) resistance, and the calculator returns the heat-sink resistance you need, the allowed total resistance and the case and sink temperatures at the limit, with a plain-language hint about what kind of heat sink that implies.
A second tab estimates an extruded finned heat sink from its width, length, fin count, thickness, height and base thickness, the material (6063 or 6061 aluminium, copper, die-cast) and an airflow setting, using straight-fin efficiency η = tanh(mH)/(mH) to find the effective area and the resulting thermal resistance, with warnings about fin spacing and efficiency. A third tab gives conduction through a thermal pad or paste (R = t/kA) and the heat generated by a linear regulator, (Vin − Vout) × I.
3 steps to your result
Open the tool and follow along. Nothing to install.
What you get
From power, ambient, junction limit, Rθjc and Rθcs.
Fin efficiency, effective area, resistance, fin gap and mass.
Thermal pad conduction and linear-regulator dissipation.
Fin spacing for natural convection, efficiency and margin advice.
AZRS tools are free to open and use.
It opens in your browser, so there is nothing to download.
Used for
Pick one to see how it fits.
How it compares
A plain look at this tool next to the usual alternative.
| This engineering calculator | Desktop software | |
|---|---|---|
| Install | Nothing to install | Usually an app or program to install |
| Account | No signup | Depends on the product |
| Cost | Free to use | Free or paid, depends on the product |
| Where it runs | In your browser tab | On your computer |
Questions people ask
What is Rθjc?
Junction-to-case thermal resistance from the component datasheet.
What h should I use?
About 5–10 W/m²K in still air, 20–60 with a small fan.
Is the fin estimate exact?
It is a first-order estimate; verify with the manufacturer's curve.
Is it free?
Yes.
How do I use the Heat Sink & Thermal Resistance Calculator?
1. Enter power, ambient and junction limit with the thermal resistances. 2. Read the heat-sink resistance you need. 3. Use the finned sink tab to try dimensions and airflow. 4. Check the interface and regulator heat on the last tab.
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Try the Heat Sink & Thermal Resistance Calculator now
Required heat-sink thermal resistance, finned heat-sink estimate, interface conduction. Free to use.
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