PSU Wattage Calculator
Size a power supply from component draw with headroom and efficiency.
About PSU Wattage Calculator
Modern GPUs produce transient spikes well above their rated draw, which is why headroom is a stability requirement rather than future-proofing. Running near 50 per cent load also places the PSU at its efficiency peak. Transient spikes trip protection circuits on marginal supplies, producing shutdowns under load that look like GPU faults rather than power problems.
Formula
PSU Wattage
Recommended rating = component draw × (1 + headroom); wall draw = draw ÷ efficiency
- headroom
- Covers transient GPU spikes that far exceed rated draw
- efficiency curve
- PSUs are most efficient around 50 per cent load
Worked example
With the default values below, PSU Wattage Calculator returns Recommended PSU Rating of 716. Change any input above and every figure here is recalculated in your browser.
Inputs used
- CPU power drawminimum 0 W
- 125 W
- GPU power drawminimum 0 W
- 320 W
- Other componentsminimum 0 W
- 85 W
- Headroom for transients and upgradesaccepts 0–100 %
- 35 %
- PSU efficiency at loadaccepts 50–99 %
- 90 %
Results
- Recommended PSU Rating
- 716 W
- Total Component Draw
- 530 W
- Power Drawn From the Wall
- 588.9 W
- Load at the Recommended Rating
- 74.02%
- Nearest Standard PSU Size
- 750 W
Step by step
- 1Values used
- 2PSU Wattage
- 3Recommended PSU Rating= 716 W
- 4Total Component Draw= 530 W
- 5Power Drawn From the Wall= 588.9 W
- 6Load at the Recommended Rating= 74.02
- 7Nearest Standard PSU Size= 750 W
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is PSU Wattage calculated?
Recommended rating = component draw × (1 + headroom); wall draw = draw ÷ efficiency Modern GPUs produce transient spikes well above their rated draw, which is why headroom is a stability requirement rather than future-proofing. Running near 50 per cent load also places the PSU at its efficiency peak.
Why does PSU Wattage matter?
Transient spikes trip protection circuits on marginal supplies, producing shutdowns under load that look like GPU faults rather than power problems.
What values do I need to enter?
This calculator takes 5 inputs: CPU power draw, GPU power draw, Other components, Headroom for transients and upgrades, PSU efficiency at load. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.