TO-220 Heatsink Calculator
How big a heatsink does a TO-220 need? The ~1.5 W bare-package ceiling, θ(sa) sizing math, insulator-pad tax and full-pack gotchas — solved live.
Preset: 10 W in a 40 °C enclosure, Tj held to 110 °C (150 − 40 margin), θjc 1.5 °C/W, paste mounting → θ(sa) ≤ 5 °C/W. Enter YOUR device's θjc from the datasheet — it spans 0.5 to 3 °C/W across TO-220 parts.
TO-220 Heatsink Calculator computes the heatsink thermal resistance a TO-220 package needs, including the bare-package (no heatsink) check — free, instant and private in your browser. Power-electronics builders sizing sinks for MOSFETs, regulators and audio outputs use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About TO-220 Heatsink Calculator
TO-220 Heatsink Calculator computes the heatsink thermal resistance a TO-220 package needs, including the bare-package (no heatsink) check using the standard engineering relation: θ(sa) = (Tj − Ta)/P − θ(jc) − θ(cs), with bare TO-220 θ(ja) ≈ 62 °C/W. Worked live: 10 W in 40 °C enclosure air with Tj held to 110 °C needs θ(sa) ≤ 5 °C/W — a 50 mm finned extrusion, not a clip-on flag. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use TO-220 Heatsink Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use TO-220 Heatsink Calculator?
- ✓Implements the real formula — θ(sa) = (Tj − Ta)/P − θ(jc) − θ(cs), with bare TO-220 θ(ja) ≈ 62 °C/W — with the substitution shown, not a black box
- ✓Built for power-electronics builders sizing sinks for MOSFETs, regulators and audio outputs
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate to-220 heatsink?+
The heatsink thermal resistance a TO-220 package needs, including the bare-package (no heatsink) check follows θ(sa) = (Tj − Ta)/P − θ(jc) − θ(cs), with bare TO-220 θ(ja) ≈ 62 °C/W. For example, 10 W in 40 °C enclosure air with Tj held to 110 °C needs θ(sa) ≤ 5 °C/W — a 50 mm finned extrusion, not a clip-on flag. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Why does the datasheet say 75 W but the bare package only handles ~1.4 W?+
The front-page rating assumes the case held at 25 °C — an infinite heatsink. Bare in still air the package's own 62 °C/W dominates: (125−40)/62 ≈ 1.4 W. Every real design lives between those extremes, and the heatsink you bolt on decides exactly where. This calculator computes that honest middle number.
How much does an insulating pad cost me thermally?+
A silicone pad adds ~1 °C/W case-to-sink versus ~0.5 for bare tab + paste. At 10 W that's 5 °C of extra junction temperature — usually acceptable, but at 30 W it's 15 °C, which is why high-power designs prefer tab-grounded topologies, aluminium-nitride pads, or isolating the whole heatsink instead of the device.
Is the TO-220 Heatsink Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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