Softonic

Power Supply Calculator

Step 1 / 3 Recommended capacity

Enter each component

Next

A power supply unit (PSU) is rated in watts, and the right rating depends on how much electricity the parts in your case actually draw. This calculator starts from the wattage you enter for each component, adds a headroom margin you choose, and recommends a capacity rounded up to a common PSU size. It is a sizing estimate, not a guarantee: it cannot tell you whether a specific PSU is physically or electrically compatible with your build.

How the estimate works

  1. 1

    Enter each component wattage

    Start from the power consumption of the parts that matter most: the CPU, the graphics card, the RAM, the motherboard, the storage drives and the fans. Most component pages list a typical or maximum wattage; use the figure that best matches your use.

  2. 2

    Choose a headroom margin

    The headroom is extra capacity added on top of the total load so the PSU is not running at its limit. Ten to twenty percent is a common range for a desktop build.

  3. 3

    Read the recommended capacity

    The estimate adds your headroom to the total and rounds up to the nearest 50 W, which matches common PSU sizes. Use it as a starting point, then check the specific PSU you are considering.

The formula

Add every component wattage to get the estimated load:

Total = CPU + GPU + RAM + Motherboard + Storage + Cooling + Other

Then add the headroom percentage h and round up to the nearest 50 W:

Recommended = ceil(Total × (1 + h / 100) / 50) × 50

A worked example

A gaming build with a 65 W CPU, a 250 W graphics card, 15 W of RAM, a 40 W motherboard, 10 W of storage, 10 W of fans and cooling, and nothing else, adds up to 390 W. With 15% headroom:

390 W × 1.15 = 448.5 W → rounded up to 450 W

A 450 W unit covers that build comfortably. The same build with a 350 W GPU would total 490 W, need 563.5 W with 15% headroom, and land on a 600 W recommendation.

Typical component loads (approximate)

Component Typical draw Notes
CPU 25 to 180 W Low-power chips draw little; high-end desktop CPUs can approach 180 W under load
GPU / graphics card 75 to 450 W The single biggest number in gaming builds; check the model’s power draw
RAM 3 to 15 W Scales with capacity and speed modules
Motherboard 20 to 60 W Includes chipset, LAN and USB controllers
Storage drives 3 to 15 W SSD drives draw less than high-RPM mechanical drives
Fans and cooling 3 to 25 W A handful of fans adds little; liquid cooling pumps add a bit more

These are planning ranges, not specifications. Real draw depends on the exact model, voltage, clocks and load.

Common pitfalls

  • Underestimating the graphics card. Transient (instantaneous) spikes from high-end GPUs can briefly exceed the continuous rating of the PSU. A comfortable headroom reduces the chance that a spike trips the unit.
  • Treating the estimate as a compatibility check. The wattage is only part of the story: connectors, physical size, and their electrical behavior matter too.
  • Ignoring efficiency. Two PSUs with the same wattage can differ in efficiency and quality. The rating is a capacity estimate, not a quality grade.
  • Adding headroom twice. If you already chose a power supply with overhead, do not add the same margin again on top.

Frequently Asked Questions

No. The numbers you enter stay in this browser. The calculation runs locally on the page, nothing is sent to our servers and nothing is added to the page link.

Ten to twenty percent is the usual range for a desktop build. Use the top of that range if you plan to overclock, add drives or upgrade the graphics card later, or if the GPU is known for transient spikes. Zero is only a lower bound, never a recommendation.

No. The result is a capacity estimate based on the wattages you enter. It does not cover connectors, physical dimensions, voltage regulation or transient behavior, so always confirm the specific unit works with the parts you chose.

Because power supplies are sold in common stepped sizes such as 300, 350, 400, 450, 500, 550 and 600 W. Rounding up to the next step gives a recommendation that matches what you can actually buy.

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