PC Power Supply Calculator

Written byOleh Soloninupdated 5 October 2026

Processor draw, W

Graphics card

Your own figure for the card, W

Leave at 0 to use the list.

Drives

Counted at 8 W per drive under load.

Fans

Counted at 3 W per fan.

Other components, W

Board, memory and peripherals. Sixty watts is a rough estimate; refine it for your own parts.

Headroom, %

Result

Recommended unit, W550
Build draw, W416
With headroom, W541
Processor, W125
Graphics card, W200
Half the rating, W275
How it adds up125 + 200 other 60 + drives 16 + fans 15 = 416 W
What matters
80 PLUS certification tests a unit's efficiency at 20, 50 and 100 percent load. Where your model peaks shows on its efficiency curve, from the maker or a review.

Headroom is not only about reliability

Adds up a build's draw from its components and picks a power supply rating with sensible headroom.

Sizing a power supply exactly is wrong for two reasons. The obvious one: a graphics card's transient peaks exceed its rated draw, and a marginal unit trips its protection. The less known one: efficiency depends on load, and 80 PLUS asks more of it at half load than at full load.

So the calculator allows thirty percent of headroom: the unit does not run at its limit, and short spikes do not trip its protection. Where a particular model peaks in efficiency shows on its own curve.

How to use

Enter the processor draw — the rated figure under load, not at idle.
Pick the graphics card from the list or type your own wattage; your own figure overrides the list.
Set the number of drives and fans and the watts for everything else — board, memory and peripherals.
Leave headroom for short spikes from the graphics card and the processor.

What a build's draw is made of

Each row is a run of this calculator with two drives, five fans, 60 watts for other components and 30 percent headroom. The per-drive and per-fan watts are the calculator's own assumptions, stated in the field help; everything else sits in its own field so you can correct it.

The graphics card decides almost everything: 525 watts separate the entry card from the flagship, while drives, fans and the rest together contribute 91 watts to any build. The recommended rating comes from the range of units actually sold — the nearest one that covers the draw with headroom.

Runs of this calculator with two drives, five fans, 60 W for other components and 30% headroom.
Graphics card	Processor	Draw	With 30% headroom	Unit	Half the rating
entry, 75 W	65 W	231 W	300 W	400 W	200 W
mid-range, 200 W	125 W	416 W	541 W	550 W	275 W
upper mid-range, 300 W	125 W	516 W	671 W	750 W	375 W
high end, 400 W	170 W	661 W	859 W	1,000 W	500 W
flagship, 600 W	250 W	941 W	1,223 W	1,600 W	800 W

What this calculator shows

The total draw of the build from its components
A recommended rating from the standard range
Half the rating, to compare with the unit's efficiency curve

What to keep in mind

Board, memory and peripherals are covered by a 60 watt baseline; drives count 8 watts each and fans 3.
Overclocking is not modelled: it raises processor and graphics draw by tens of percent.

FAQs

How much headroom should a power supply have?

Twenty to thirty percent above the calculated draw. More does no harm but rarely justifies the price.

What happens with an undersized unit?

The machine shuts down under load — usually in games, where the graphics card peaks. It often looks like a reboot with no error message.

How much does a gaming PC draw?

It depends on the parts. The scenarios in the table above run from 231 to 941 watts without overclocking; those are runs of this calculator, not a survey of gaming PCs.

Does the 80 Plus rating affect the wattage I need?

Not the rating you need, but it does affect the electricity bill and the heat. A higher certification means less loss to heat at the same delivered power.

Why leave headroom if the unit already copes?

Because draw is not steady: short spikes from the card and the processor run above the average figure, and the unit has to ride them out without sagging. On top of that, 80 PLUS asks for higher efficiency at half load than at full load.

Where do the watts for drives and fans come from?

They are the calculator's own assumptions, stated in the field help: 8 watts per drive under load and 3 watts per fan. Board, memory and peripherals sit in a separate field set to 60 watts — if you know your own numbers, put them in.

Worked example

A mid-range gaming build

Input: 125 W processor, mid-range graphics, 2 drives, 5 fans

Output: 416 W of draw, so a 550 W unit fits

Note: With thirty percent headroom the requirement is 541 watts, and the nearest standard rating is 550. At the build's full draw that is 76 percent of the rating; check the particular unit's curve for its efficiency peak.

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Result

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