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PC power supply calculator: what wattage should you choose?

Choose your processor, graphics card and the rest of your build: the calculator estimates the maximum power draw, breaks it down by component and recommends the right power supply wattage, taking graphics card makers' recommendations into account.

Hardware Tool All levels Published October 20, 2026 Translated October 27, 2026 3 min read Version française
PC power supply unit with its cables on a yellow background
Photo: Andrey Matveev on Unsplash

In plain words

The power supply is the PC's electricity meter. Too weak, it cuts out or crashes the machine as soon as the game or render starts; oversized, it costs more and brings nothing. The calculator adds up the maximum power draw of each part, then adds the margin you need. Everything is calculated in your browser.

How the calculation works

Item Value used
Processor Its maximum sustained power: PPT for AMD (1.35 times the advertised TDP), Maximum Turbo Power or PL2 for Intel
Graphics card Its reference power (TGP for Nvidia, TBP for AMD)
Motherboard 30 to 65 W depending on form factor and features (chipset, power stage, network, audio)
Memory 5 W per DDR5 module
Storage 8 W per NVMe SSD, 4 W per SATA SSD, 10 W per hard disk in operation
Fans, USB, pump, RGB 3 W per fan, 2.5 W per USB device, 6 W for a pump, 15 W for heavy lighting
Margin 30% above the total (40% when overclocking), and never less than the graphics card maker's recommendation

The margin is not waste: a power supply is most efficient and quietest between 40 and 75% of its rating, and modern graphics cards cause power spikes lasting a few milliseconds well beyond their rated power.

Quality matters more than watts

A good 750 W power supply is better than a mediocre 1,000 W one. Rely on independent reviews, efficiency certifications (80 PLUS Gold or Cybenetics), the ATX 3.1 standard for powerful graphics cards and a long warranty. The criteria are detailed in What each PC component does.

Limits of the estimate

  • The values are those of reference models. A factory-overclocked graphics card often draws 5 to 15% more: in that case, enter its exact power in the free field, from the manufacturer's spec sheet.
  • A processor can exceed its rated power if the motherboard lifts the stock limits (a common option on high-end boards): check this setting in the BIOS.
  • To know the real power draw, nothing beats a power meter plugged into the socket.

Once the power supply is chosen, the tutorial Building your PC step by step explains how to install it and connect the cables.

Sources

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