Formula
Drives and fans are counted, then everything is summed:
watts = CPU + GPU + drive watts × drives + fan watts × fans + board
The PSU page divides a load by efficiency and adds headroom. This page is only the sum.
Assumptions
- Each watt figure is the draw you want to allow, not a measured peak unless you typed one.
- Every drive uses the same watts.
- Every fan uses the same watts.
Worked example
A 125 W CPU, a 200 W GPU, two 8 W drives, four 3 W fans, and 50 W for the board total 403 W.
Input definitions
- Board and the rest
- Motherboard, memory, and anything else you fold into one allowance.
- Component total
- The sum of those allowances, before a power-supply loss.
Limitations
This is a planning figure from the numbers you type. It is not a measurement of a network, a camera, a printer, or a power supply.
Questions
Is this the size of supply to buy?
No. Take the total to the PSU page, which applies efficiency and headroom and then picks a catalog size.
Can fans be zero?
Yes. A zero count or zero watts drops that term out of the sum.