Computers & Laptops

PC Power Calculator

Add up what your PC's components draw, and see the supply capacity that total suggests.

25 inputs Free, no sign-up

Your figures

Name each component and enter its power from the manufacturer's specification. Leave a row blank to skip it.

Spare capacity above the total. A choice, not a rule - set it to zero to see the bare figure.

Try an example

Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

A PC's power draw is the sum of its parts, and the parts are the only place the numbers can come from. Enter what each component is specified at and this page adds them up, sorts them by size, and shows the supply capacity the total suggests once you have allowed some headroom.

No wattage is filled in for you. A processor can be 35 W or 250 W depending on which one it is, and a graphics card covers an even wider range — so a figure invented for a category would be wrong for most readers of it.

How to use this calculator

  1. Find each component's rated power. For a processor it is usually quoted as TDP or base power; for a graphics card, as total board power or the manufacturer's recommended supply figure.
  2. Enter each one on its own row, with how many of that part you have.
  3. Leave any row blank to skip it. Nothing is assumed for a row you do not fill in.
  4. Set the headroom you want above the total, or zero to see the bare sum.

Already know your total? The PSU wattage calculator takes it directly, and the PSU load calculator checks it against a supply you already own.

The formula

Total load        = sum of (each component's power x how many)
Suggested supply  = Total load x (1 + headroom / 100)

The headroom is a choice. The common advice to size a supply at roughly twice the load comes from efficiency curves peaking near half load and from leaving room for a later upgrade, and neither is a specification.

SymbolMeaningUnit
Component power What each part is rated at W
Quantity How many of that part
Headroom Spare capacity you want %

Worked example

A processor at 120 W, a graphics card at 250 W, a board at 50 W, memory at 10 W, two drives at 6 W each and five fans at 3 W:

120 + 250 + 50 + 10 + 12 + 15 = 457 W
457 x 1.30                     = 594 W

So a 600 W supply covers it with the headroom asked for.

Notes and limits

  • Rated power is a sustained figure. Modern processors and graphics cards draw considerably more than their rating for a few milliseconds at a time, and a supply has to ride those spikes as well as the average.
  • This assumes everything draws its rated power at once, which is the right assumption for sizing a supply and a pessimistic one for predicting a bill. For the bill, use the PC electricity cost calculator.
  • The figure is a wattage, not a product. Connectors, physical size, protections and build quality all matter when choosing a supply and none of them is a number.
  • Peripherals powered from USB draw from the supply too, though rarely enough to change the answer.

What this calculation assumes

  • Every wattage is one you entered. No component specification is stored in this page.
  • Everything is assumed to draw its rated power at the same time, which is the safe assumption for sizing a supply.
  • The headroom is your choice and the result names the figure it used.

Frequently asked questions

How do I work out what my PC draws?

Add up the rated power of each component - processor, graphics card, motherboard, memory, drives, fans and cooling. The figures are in each part's specification. A plug-in energy meter measures what the whole machine actually draws, which is usually well below the sum of the ratings.

Where do I find my processor or graphics card wattage?

On the manufacturer's product page for the exact model. Processors quote TDP or base power; graphics cards quote total board power, and often a recommended system supply figure as well. This page does not hold those numbers, because they change with every generation.

How much headroom should I leave?

Enough that the supply is not running at its limit and there is room for a later upgrade. Beyond that it is a judgement rather than a rule, which is why the field is yours to set.

Is the sum of the ratings what my PC actually uses?

No - it is the worst case. Real draw is lower most of the time, because components rarely all sit at maximum together. That makes it the right figure for sizing a supply and the wrong one for estimating electricity cost.

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