PC Power Supply Calculator
Estimate the power supply wattage a PC build needs from its components.
About the PC Power Supply Calculator
Enter the CPU's maximum power, the graphics card's board power, the number of drives and fans, other devices and the headroom you want. The calculator gives the estimated peak load and the next standard PSU size, with a chart of power by component.
Add up maximum component power, about 60 W for motherboard and memory, and a few watts each for drives and fans. Add 30–50% headroom; modern GPUs can spike well above their rating for milliseconds, and PSUs run most efficiently around 50% load.
The formula
PSU ≥ Σ component power × (1 + headroom)
Worked example
A 125 W CPU and 285 W GPU, 2 drives, 4 fans, 20 W of extras
- Peak load: 125 + 285 + 16 + 12 + 20 + 60 = 518 W
- With 40% headroom: 725 W
- Recommended: a 750 W PSU
Questions people ask
Is a bigger PSU wasteful?
Not much; efficiency is fairly flat between 20% and 80% load.
Does the GPU maker's recommendation differ?
They often suggest more to cover weaker PSUs; follow it if unsure.
Does the 80 Plus rating matter?
It shows efficiency: Gold wastes less power as heat than Bronze, which saves a little electricity and noise.