PSU Size Calculator
Enter the CPU and graphics card power, the number of drives and fans, and whether you overclock. The calculator estimates the full load, adds headroom for power spikes and suggests a power supply size and efficiency rating.
- PSU wattage
- Full load
- Headroom
Use the CPU's maximum turbo power and the graphics card's total board power from the maker.
The graphics card is usually the biggest load in a gaming PC. Add up the parts, then size the supply so the full load sits at about 70% of its rating. A 125 W CPU and a 300 W graphics card with a few drives and fans draw about 530 W, so a 750 W power supply is a sensible choice.
PSU size chart
125 W CPU, 2 drives, 4 fans. Search for a GPU.
| GPU power (W) | Full load (W) | PSU (W) |
|---|---|---|
| 0 | 227 | 450 |
| 75 | 302 | 450 |
| 150 | 377 | 550 |
| 200 | 427 | 650 |
| 250 | 477 | 750 |
| 300 | 527 | 750 |
| 350 | 577 | 850 |
| 450 | 677 | 1000 |
| 600 | 827 | 1200 |
Rounded up to a common size.
Graphics card and PSU
125 W CPU. Slide the graphics card power.
The bar shows each part's share of the power supply.
How to size a power supply
Parts to watts. Step through it.
CPU
Turbo power.
Look for a quality supply with protections. A cheap one can fail and take parts with it.
Bronze, Gold or Platinum
Efficiency ratings. Compare them.
Budget.
Common.
Premium.
Higher efficiency wastes less power as heat, so the supply runs cooler and quieter.
Before you buy
PSU checks. Tick each item.
Tick each item as you go.
Check the supply has the right GPU power connectors, including the newer 16-pin type.
What you get
PSU sizing. Each tile explains one result.
Watts.
Full.
Per cent.
Efficiency.
Running.
Power supplies are most efficient at around half load, which also keeps the fan quiet.
Frequently Asked Questions
No question matches that search.
What size power supply do I need?
Add up your parts' power and multiply by about one point four, then round up to a common size.
Is a bigger power supply bad?
No, but it costs more and may be slightly less efficient at low load.
How much power does a graphics card use?
From about seventy-five watts for small cards to four hundred and fifty or more for the fastest.
What happens if my PSU is too small?
The PC may shut down or restart under heavy load.
Do I need extra headroom for power spikes?
Yes. Modern graphics cards can briefly draw far more than their rating.
Which efficiency rating should I choose?
Gold is a good balance for most gaming PCs.
Does overclocking need a bigger PSU?
Yes, allow about a fifth more.
Power with room to spare
Size the supply to your parts with good headroom, and your PC runs stable and quiet.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.