Heatsink Calculator (required θsa)
The heatsink thermal resistance you must buy — from power, Tj target, ambient and the junction-to-case chain.
Heatsink catalogue ratings assume free vertical fins in open air — inside a box with no airflow, derate ~30–50 %. Forced air transforms the picture: even 1 m/s roughly halves θ(sa). If the result says “impossible”, the package (θjc) is the bottleneck — parallel devices or a switch-mode design beats any heatsink.
Heatsink Calculator computes the heatsink thermal resistance (θsa) your device needs — free, instant and private in your browser. Power-supply, amplifier and motor-driver designers picking a heatsink that actually fits the budget 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 Heatsink Calculator (required θsa)
Heatsink Calculator computes the heatsink thermal resistance (θsa) your device needs using the standard engineering relation: θ(sa) ≤ (Tj − Ta)/P − θ(jc) − θ(cs). Worked live: 15 W with Tj capped at 100 °C in 40 °C air, θjc 1.5 and paste 0.5 → buy a heatsink under 2.0 °C/W. 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 Heatsink Calculator (required θsa)
- 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 Heatsink Calculator (required θsa)?
- ✓Implements the real formula — θ(sa) ≤ (Tj − Ta)/P − θ(jc) − θ(cs) — with the substitution shown, not a black box
- ✓Built for power-supply, amplifier and motor-driver designers picking a heatsink that actually fits the budget
- ✓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 heatsink?+
The heatsink thermal resistance (θsa) your device needs follows θ(sa) ≤ (Tj − Ta)/P − θ(jc) − θ(cs). For example, 15 W with Tj capped at 100 °C in 40 °C air, θjc 1.5 and paste 0.5 → buy a heatsink under 2.0 °C/W. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
What do heatsink °C/W ratings actually promise?+
Catalogue θsa assumes free vertical fins in open still air. Inside an enclosure derate 30–50 %; with even gentle forced air (1 m/s) the same sink roughly halves its θ. Orientation matters too — horizontal fins lose ~20 %.
The calculator says 'impossible' — what now?+
Your package's θjc already spends the whole budget — no heatsink can fix it. Options: spread the load across parallel devices, switch to a lower-loss topology (a switcher instead of a linear), lower the ambient, or accept a lower-rated life at higher Tj.
Is the 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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