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.
PC PSU Wattage Calculator — How Big a Power Supply Do You Need?
Our free PSU wattage calculator estimates the total power draw of your PC build and recommends the minimum power supply size. Enter your CPU TDP, GPU TDP and the number of other components to get an accurate power budget — and stop buying underpowered PSUs that cause system instability, or massively oversized ones that waste money.
How PC Power Consumption is Calculated
Total system power draw is the sum of all component TDPs (Thermal Design Power ratings) plus a baseline for the motherboard, storage and fans. However, components rarely run at full TDP simultaneously — real-world gaming loads typically reach 70–90% of GPU TDP and 60–80% of CPU TDP. Our calculator uses these realistic peak figures and adds a 25% safety margin for headroom and PSU efficiency losses.
Component Power Draw Reference
- CPU: Budget (35–65W), Mid-range (65–125W), High-end (125–253W), Overclocked (250W+)
- GPU: Integrated (0W), Low-end (75W), Mid-range (150–200W), High-end (250–320W), Flagship (350–600W)
- RAM: Approximately 3–5W per stick
- SATA SSD: 2–4W per drive
- NVMe SSD: 5–10W per drive
- HDD: 6–10W per drive (spinning disks)
- Case fans: 1–3W per fan
- Motherboard: 20–80W depending on chipset and VRM
PSU Efficiency Ratings Explained
PSU efficiency ratings (80 Plus Bronze, Silver, Gold, Platinum, Titanium) indicate how much power drawn from the wall is delivered to your components. An 80 Plus Gold PSU is 87–90% efficient at 50% load. A less efficient unit wastes more power as heat and costs more to run. For a gaming PC running 6 hours/day, upgrading from 80 Plus Bronze to Gold saves approximately £15–30/year in electricity costs in the UK.