PC Power Supply Wattage Calculator
Sizing a PC power supply is straightforward arithmetic: add the rated power of every component, then add a margin so the supply is not run at its limit. Enter the wattage of your CPU, GPU, motherboard, drives and storage, fans and lighting, and any other peripherals, taken from each part's official specification. Set the headroom percentage you want above the load. This calculator returns the total component draw, the recommended PSU size with headroom, the load at that size, and the suggested rating tier. Every wattage is an editable input.
PSU wattage formula
Total load = CPU + GPU + motherboard + storage + fans + other
Recommended PSU = total load * (1 + margin / 100)
Headroom watts = recommended PSU - total load
Load at recommended = total load / recommended PSU * 100
(Round the recommended figure up to a sold PSU rating)
Aim for the supply to sit around 50 to 80 percent load for efficiency. Choose a sold size at or above the recommended figure.
Power supply context
- The GPU and CPU are usually the two largest loads in a desktop PC.
- Use each manufacturer's rated power (CPU TDP, GPU total board power) for accuracy.
- A 20 to 30 percent margin keeps the PSU off its limit and allows for upgrades.
- 80 PLUS tiers describe efficiency, not capacity; size to load plus headroom first.
- All component wattages here are editable so the result reflects your exact build.
PC power supply calculator: frequently asked questions
How do I size a PC power supply?
Add the maximum power draw of every component (CPU, GPU, drives, fans, motherboard, and peripherals), then add a headroom margin so the supply runs below its rated maximum. A common practice is to choose a PSU rated 20 to 30 percent above the summed load for efficiency and longevity.
Why add a headroom margin?
Power supplies are most efficient and reliable when loaded to roughly 50 to 80 percent of their rating, not at the limit. Headroom also covers transient spikes, future upgrades, and capacitor aging. The margin you enter is applied on top of the total component draw.
Where do I find each component's wattage?
Use the rated power (TDP for CPUs, total board power for GPUs) from the manufacturer's specification sheet. This calculator leaves every wattage as an editable input so you enter the exact figures for your parts rather than relying on generic averages.
Does PSU efficiency rating change the size I need?
Efficiency (such as the 80 PLUS tiers) affects how much wall power is drawn and heat produced, not the DC wattage your components need. Size the PSU to the component load plus headroom; efficiency then determines running cost and thermals.
Why are all the wattages user-editable?
Component power draw varies by exact model, clock speed, and load, which we cannot know for you. Hardcoding a figure would risk an untrue number. Instead you enter each part's rated wattage from its official spec sheet, and the tool sums them with your chosen margin.
Official sources
- U.S. Environmental Protection Agency: ENERGY STAR program for power supplies and computers.
- U.S. Department of Energy: Energy use and efficiency reference.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.