7805 Heatsink Calculator
Linear-regulator heat math: P = (Vin−Vout)·I — find out whether your 7805 needs a heatsink, what size, and when a buck module should replace it.
Preset: 12 V → 5 V at 500 mA (the Arduino-era classic) → 3.56 W of heat, heatsink mandatory: θ(sa) ≤ ~11 °C/W. Also try Vin = 9 (halves the heat) and Vin = 7.5 (near-dropout — remember the 7805 needs Vin ≥ 7 V).
7805 Heatsink Calculator computes the heat a 78xx linear regulator dissipates and whether it needs a heatsink — with the exact θ(sa) if so — free, instant and private in your browser. Hobbyists and repair techs deciding between a heatsink and a buck module 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 7805 Heatsink Calculator
7805 Heatsink Calculator computes the heat a 78xx linear regulator dissipates and whether it needs a heatsink — with the exact θ(sa) if so using the standard engineering relation: P = (Vin − Vout)·I + Vin·Iq, then θ(sa) = (Tj − Ta)/P − θ(jc) − θ(cs) with 78xx θja 65, θjc 5 °C/W. Worked live: the Arduino-era classic — 12 V in, 5 V out at 500 mA — wastes 3.56 W at 42 % efficiency: heatsink mandatory, θ(sa) ≤ ~11 °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 7805 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 7805 Heatsink Calculator?
- ✓Implements the real formula — P = (Vin − Vout)·I + Vin·Iq, then θ(sa) = (Tj − Ta)/P − θ(jc) − θ(cs) with 78xx θja 65, θjc 5 °C/W — with the substitution shown, not a black box
- ✓Built for hobbyists and repair techs deciding between a heatsink and a buck module
- ✓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 7805 heatsink?+
The heat a 78xx linear regulator dissipates and whether it needs a heatsink — with the exact θ(sa) if so follows P = (Vin − Vout)·I + Vin·Iq, then θ(sa) = (Tj − Ta)/P − θ(jc) − θ(cs) with 78xx θja 65, θjc 5 °C/W. For example, the Arduino-era classic — 12 V in, 5 V out at 500 mA — wastes 3.56 W at 42 % efficiency: heatsink mandatory, θ(sa) ≤ ~11 °C/W. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
What's the quickest way to reduce 7805 heat without a heatsink?+
Drop Vin — heat is (Vin−5)×I, so feeding from 9 V instead of 12 V cuts dissipation 43 % at the same load, and from 7.5 V (just above the 2 V dropout) by 64 %. Series-dropping with a power resistor or pre-regulating with a buck to ~7 V are the classic tricks that let the 7805 keep its clean, quiet output.
Why does my 7805 circuit reboot in a slow on-off cycle?+
Thermal shutdown: the junction hits ~150–170 °C, the regulator cuts out, cools, restarts — a sawtooth that masquerades as a firmware bug. The 78xx survives it (it's internally protected) but your circuit doesn't. Compute the dissipation honestly, fit the indicated heatsink, or move to a buck converter.
Is the 7805 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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