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PC Build Wattage & PSU Calculator

Add up your CPU, GPU, storage, fans, and RAM to estimate total system draw, then get a recommended PSU wattage with headroom for transient spikes, plus the running electricity cost.

When to use this

Use this when planning a new PC build or checking whether an existing PSU has enough headroom for a GPU upgrade, before you commit to buying a specific power supply.

How it compares

Unlike simply picking a round PSU wattage based on GPU tier, this calculator builds up your actual component list, adds a headroom margin for transient spikes, and estimates the ongoing electricity cost of running the system.

Enter your values below. Calculations run locally as you type.

How it works

Component wattage is summed from your CPU and GPU TDP plus rough per-unit estimates for storage drives, case fans, RAM sticks, and a motherboard/misc baseline.

A headroom percentage is added on top to cover transient power spikes and any overclocking, giving a realistic system draw rather than just the sum of rated TDPs.

The recommended PSU is the smallest standard PSU size that keeps your system draw at or below about 87% of the unit’s rated capacity, leaving margin instead of running near maximum continuously.

FAQs

Why add headroom beyond my calculated wattage draw?

Modern GPUs and CPUs can briefly spike well above their rated TDP during transient load changes — sometimes 1.5–2× their steady-state draw for a fraction of a second. A PSU that is only sized for the average draw can trip or shut down during these spikes.

Why not just buy a PSU rated for exactly the wattage calculated?

Beyond transient spikes, PSUs run most efficiently at partial load, not maxed out, and buying exactly to the calculated number leaves no margin for future upgrades.

What is the PSU efficiency "sweet spot"?

Most 80 Plus-certified power supplies, especially Gold-rated and above, are most efficient between roughly 50–70% of their rated load. A wildly oversized PSU runs at very low load most of the time, which is slightly less efficient (though rarely a large cost difference).

Does this account for overclocking?

Yes — the headroom percentage is meant to cover both overclocking and transient spikes. Increase it if you plan aggressive CPU or GPU overclocks.

Worked example

Input

CPU 105W, GPU 220W, 2 drives, 3 fans, 2 RAM sticks, 40W baseline, 20% headroom, $0.16/kWh, 4 hrs/day gaming.

Output

System draw: 469W. Recommended PSU: 550W. Monthly cost: about $9.01.

Components sum to 391W (105+220+14+6+6+40). Adding 20% headroom brings system draw to about 469W. The smallest standard PSU size that keeps this at or below 87% load (469×1.15 ≈ 540W) is 550W. At 4 hours of gaming a day, electricity costs about $9.01/month.

Common pitfalls

  • Buying a PSU for exactly the calculated draw, with no headroom, leaves no margin for brief transient power spikes from the CPU or GPU under load.
  • Skipping storage drives, fans, and RAM in the tally understates total draw — these add up quickly in a build with several drives or RGB fans.
  • Assuming a bigger PSU is always better ignores the efficiency sweet spot — a wildly oversized PSU runs at very low load most of the time, which is slightly less efficient.

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