PSU Wattage Calculator
From Hardware-wiki
How to size a power supply without an online calculator lying to you.
Add up the parts
- CPU: TDP from the manufacturer (65-130 W for desktops of this era).
- GPU: board power; a mid-range card 100-150 W, high-end 200-300 W.
- Motherboard + RAM: 40-60 W.
- Each hard disk: 10 W; SSD: 3 W; optical: 20 W spinning.
- Fans, USB devices: 20 W total unless you have a lot.
Multiply by 1.3 for headroom and ageing. Then check the 12V rail amperage, not just total watts: a "600 W" unit with 20 A on 12 V is a 240 W unit for a modern system.
Rule of thumb
A quality 450-550 W unit covers almost any single-GPU build. Buy efficiency (80 Plus) over big numbers.