TAHA Engineering Toolsby TAHA Knowledge Lab

Computer & IT

PC Power Supply (PSU) Wattage Estimator

Add up PC component power, apply headroom and find a suitable power supply size.

Inputs

Use the maximum or boost power from the CPU maker’s specification, not only the base TDP, if you know it.

Total board power from the card maker. Enter 0 for integrated graphics.

Typical desktop allowance; check your parts if unsure.

Extra capacity above the estimated load for power spikes, ageing and future upgrades. 20–40% is commonly used. Your choice.

Result

Suggested minimum PSU rating
585W
Next common PSU size
600 W
Estimated component load
450W
Load as share of that PSU size
75%

The parts draw about 450 W. With headroom, choose at least 585 W — for example a 600 W unit, if that matches the maker’s recommendation.

Educational estimate — check the assumptions below.

About this calculator

A desktop power supply must deliver the combined power of all components with some spare capacity. This estimator adds the power figures you enter, applies a headroom margin and shows the next common PSU size. It is a planning aid: the graphics card maker’s recommended PSU rating and the PSU’s own specification take priority.

Formula

Load = CPU + GPU + motherboard/RAM + drives + fans + other

Suggested rating = Load × (1 + headroom)

The next size is chosen from common retail ratings (300, 350 … 1000, 1200 … 2000 W).

Worked example

CPU 125 W + GPU 220 W + board/RAM 60 W + drives 15 W + fans 15 W + other 15 W = 450 W. With 30% headroom: 450 × 1.3 = 585 W → next common size 600 W (load ≈ 75% of rating).

Assumptions and limitations

  • An estimate, not a replacement for the CPU, graphics card and PSU makers’ recommendations. Component power varies between models and settings.
  • Modern graphics cards and CPUs can draw short power spikes well above their rated power; this is one reason for the headroom.
  • PSU quality matters: check the rating on the 12 V output and the required connectors, not only the label wattage.
  • Wall power (from the socket) is higher than component power because the PSU is not 100% efficient.

References

  • Sum of component power plus a user-chosen design margin; component figures from the manufacturers’ specifications.