How the sizing works
The calculator adds up three things: the graphics card, the processor and an allowance for everything else. It then picks a power supply big enough to run that load with room to spare.
Graphics card power is the figure the chip maker publishes: Total Graphics Power for Nvidia and Typical Board Power for AMD. Where a card is sold in two versions we use the higher figure. Cards with a factory overclock can draw more than this.
Processor power is the most the chip may draw at stock settings, which is higher than the TDP on the box. For Intel that is Maximum Turbo Power. For AMD Ryzen it is the socket power limit, which is 1.35 times the TDP. Where one entry covers two processors, such as the Ryzen 5 7600 and 7600X, we use the higher of the two.
The rest of the system gets a flat 75 W for the motherboard, memory, drives and fans. A PC with many hard drives or a custom liquid cooling loop needs more.
We size the supply so that peak load is no more than 80% of its rating, then round up to the next size sold: 450, 550, 650, 750, 850, 1000, 1200 or 1600 W. The spare capacity covers the brief spikes graphics cards produce and keeps the supply away from its limit.
Nvidia and AMD also publish a minimum power supply for a PC with each card, based on their own test systems. If that is higher than our figure, we use theirs.
This is an estimate from published figures, not a measurement of your PC. Read more about how we handle data and corrections in our editorial policy.