Heat Sink Sizing Console

Heatsink sizing runs backwards from a temperature you must not exceed. The junction has a maximum it can tolerate, the air comes in at some ambient, and the difference is the entire temperature budget you have to work with. Divide that budget by the power and you get the total thermal resistance the whole path — package, interface, heatsink — is allowed. The heatsink only gets what's left after the package and the interface material take their cut.

That subtraction is where high-power parts get unforgiving. The package's junction-to-case resistance and the interface material's resistance are fixed costs against the budget, and times a large power they can consume most of it before the heatsink starts. What remains — the required sink-to-ambient resistance — can be a fraction of a degree per watt, and the smaller it is, the more aggressive the cooling must be. This console does that arithmetic and tells you which class of cooler can actually hit the number.

The cruel part is the inverse relationship with power. At a fixed budget, the allowed resistance is inversely proportional to power, so every increase in TDP tightens the requirement, and resistance is expensive to reduce — it takes disproportionately more heatsink, more airflow, or an entirely new cooling class to shave each increment. There is a hard floor where forced air simply can't go lower no matter the fan, and crossing it makes liquid cooling not a choice but a necessity. Watching the required resistance fall past that floor is how this tool tells you the air era is over for your part.

Two practical reminders. Ambient eats the budget one degree at a time, so size to the worst-case inlet, not the bench. And the interface material is a lever you control — a better TIM gives the heatsink more room. Get that term from the TIM Calculator, and confirm the assembled chain holds in the Junction Temperature console.