PC Power Supply Calculator

Processor draw, W

Graphics card

Your own figure for the card, W

Leave at 0 to use the list.

Drives

Fans

Headroom, %

Result

Recommended unit, W550
Build draw, W416
With headroom, W541
Processor, W125
Graphics card, W200
Peak efficiency at, W275
What mattersA power supply is most efficient at about half its rating, so a 30 percent margin is more than just insurance.

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 peaks at around half the rated load.

So thirty percent of headroom is not caution, it is the operating point. A 550 watt unit in a system drawing 400 runs more efficiently and more quietly than a 450 watt unit in the same machine.

What this calculator shows

The total draw of the build from its components
A recommended rating from the standard range
The load at which the unit runs most efficiently

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?

An ordinary build with a mid-range card runs 350 to 450 watts under load. A flagship card with an overclocked processor reaches 800.

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.

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. It will sit around 75 percent load, with peak efficiency near 275 watts.

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PC Power Supply Calculator

Result

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