PC Power Supply Calculator
Estimate total system draw and the power supply size you should buy, with headroom for transients and efficiency.
Your details
Use the TDP or PPT from the spec sheet
0 if you are using integrated graphics
Rest of the system
Sizing
Running cost
This calculator runs entirely on your device. Nothing you enter is uploaded, stored, or sold. How this works
Recommended PSU
750 W
System draws about 492 W under load, leaving 34% headroom
Includes your inputs, the full breakdown, and every row of the table.
Estimated load
492 W
With headroom
689 W
PSU utilisation at load
66%
Running cost per year
$275
- CPU
- 125 W
- Graphics card
- 300 W
- Motherboard and chipset
- 50 W
- Memory
- 6 W
- Storage
- 5 W
- Fans
- 6 W
- Total under load
- 492 W
| Period | Energy | Cost |
|---|---|---|
| Per day | 4.43 kWh | $0.75 |
| Per month | 132.8 kWh | $22.58 |
| Per year | 1,616 kWh | $275 |
What this means
- Power supplies are most efficient at roughly half load, so sizing for about 50-60% utilisation under load is both efficient and quiet — the fan barely spins.
- Modern graphics cards draw brief spikes well above their rated power. A unit with genuine headroom rides these out; a marginal one trips its protection and the machine reboots under load.
- Buy on the quality of the unit, not just the wattage. An 80 Plus Gold rating from a reputable manufacturer at 750 W is a better purchase than an unbranded 1000 W.
How the pc power supply calculation works
Sizing a power supply is mostly about the two components that dominate the budget: the processor and the graphics card, which together usually account for eighty percent or more of the total. Everything else — board, memory, drives, fans — adds up to something in the region of seventy to ninety watts on a typical desktop, which is why guessing the rest rarely changes the answer.
The reason to leave headroom is not that the numbers are wrong but that the load is not steady. Graphics cards in particular draw very short spikes far above their rated figure, and a supply running close to its limit will hit over-current protection and shut the machine down rather than ride them out. Headroom also buys efficiency and silence, because supplies run coolest and quietest around half load, and it leaves room for the upgrade you will eventually make.
Frequently asked questions
Does a bigger power supply use more electricity?
No. The system draws what it needs and the supply delivers that; the rating is a ceiling, not a consumption figure. A larger unit running at 40% load is often slightly more efficient than a smaller one straining at 90%, so the oversized unit can actually cost marginally less to run.
Why does my PC restart during games but not at the desktop?
That is the classic symptom of a supply without enough headroom. Gaming loads the CPU and graphics card simultaneously, and the transient spikes from a modern card can briefly double its rated draw. The supply's protection circuitry sees an overload and cuts power rather than risk damage.
What does the 80 Plus rating mean for me?
It certifies efficiency — how much of the wall power reaches your components instead of becoming heat. A Gold unit wastes around ten percent, a basic one considerably more. Higher ratings mean lower bills and less heat in the case, and they generally correlate with better internal components, though the rating itself only measures efficiency.
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Disclaimer. This calculator is provided for general information and educational purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Results are estimates based on the inputs you provide and the assumptions described above. Confirm any figure with a qualified professional before acting on it.