PSU RULE OF THUMB
Always choose a PSU rated for at least 20–30% more than your estimated draw. This improves efficiency, runs cooler, and gives headroom for upgrades. A quality 80 Plus Gold or Platinum rated PSU at 650–850W suits most gaming/workstation builds.
PSU Wattage Calculator
Undersize a PSU and you get random reboots under load, coil whine, or a system that won't post with a new GPU installed. Oversize it by a huge margin and you're paying more upfront and running at lower efficiency for years. This estimates actual power draw from your CPU, GPU and component count so you land somewhere sensible in between.
Why "just add up the TDPs" overestimates
Components rarely all hit their rated TDP simultaneously in real workloads — gaming loads typically land around 70–90% of GPU TDP and 60–80% of CPU TDP at the same time, not both pinned at 100% together. This calculator works off those realistic peak figures rather than the worst-case sum, and adds roughly 25% headroom on top for safety margin and PSU efficiency losses, rather than forcing you to buy for a scenario your system will basically never hit.
Rough power draw by component
- CPU — budget 35–65W, mid-range 65–125W, high-end 125–253W, overclocked can push past 250W
- GPU — integrated is effectively 0W, low-end ~75W, mid-range 150–200W, flagship cards 350–600W+
- Storage — SATA SSD 2–4W, NVMe 5–10W, spinning HDD 6–10W
- RAM — roughly 3–5W per stick
- Motherboard — 20–80W depending on chipset and VRM design, easy to forget when you're mentally adding up "just the CPU and GPU"
Efficiency ratings actually cost you money over time
80 Plus Bronze/Silver/Gold/Platinum/Titanium ratings tell you how much of the power drawn from the wall actually reaches your components — a Gold unit runs roughly 87–90% efficient at half load, meaning less waste heat and a lower electricity bill than a Bronze unit doing the same job. For a gaming PC running six hours a day, jumping from Bronze to Gold works out to somewhere around £15–30 a year in the UK — not huge on its own, but it compounds, and a more efficient PSU also tends to run cooler and quieter under sustained load.