You look at measured draws for the relevant workloads. Anandtech has a good intro to the various states that an Intel CPU can be in here: https://www.anandtech.

You look at measured draws for the relevant workloads. Anandtech has a good intro to the various states that an Intel CPU can be in here: https://www.anandtech.com/show/13544/why-intel-processors-draw-more-power-than-expected-tdp-turbo https://www.anandtech.com/show/13544/why-intel-processors-dr... For Intel specifically the TDP is what you need to dissipate to sustain the base frequency. If you want to run beyond base frequency (the "all core turbo"), then you need to handle more. How much more isn't officially documented, nor are the turbo charts either annoyingly (aka, this: https://en.wikichip.org/wiki/intel/core_i9/i9-9900k#Frequencies https://en.wikichip.org/wiki/intel/core_i9/i9-9900k#Frequenc... ) So for a 9900K looking the official numbers are 95W for 3.6GHz of all core load. But it'll turbo with all cores loaded up to 4.7GHz, for which you'll need some amount of cooling. How much? Well more than 95W that's for sure, but that's all you really officially know. So then you look at reviews and you find that under full load the 9900K pulls down ~170W if it's not hitting thermal limits: https://images.anandtech.com/graphs/graph14605/111362.png https://images.anandtech.com/graphs/graph14605/111362.png