Add your parts and this estimates peak power draw for the whole system, then recommends a power supply with comfortable headroom. Use it before you buy – a PSU that's too small is the #1 cause of random shutdowns under load.
Estimates use typical component power draw, not worst-case transient spikes – cards like the RTX 4090/5090 can momentarily spike well above their TDP, so when in doubt, go one size up.
How we calculate this – assumptions & formulas
Not a lab measurement – a conservative peak estimate so you don't trip under load. Transient spikes (especially on RTX 4090/5090) can still exceed TDP briefly.
1. Peak draw
peak = (cpu + gpu + ram×3W + ssd×3W + hdd×8W + fans×3W + aio + rgb×4W + usb×5W) × age_factor
CPU/GPU use TDP presets (e.g., i7/R7 125 W, RTX 4090 450 W, RX 7900 XTX 355 W) or your custom wattage. Small parts are averaged per unit: RAM stick 3 W, NVMe 3 W, HDD 8 W, fan 3 W, AIO pump 8 W, RGB strip 4 W, USB device 5 W.
2. Recommended PSU
recommended = ceil(peak × 1.30 / 50) × 50
30% headroom for efficiency, noise, and aging, then rounded up to the next 50 W tier (the common retail step). If age_factor is 1.1 (a few years old) or 1.25 (older/budget unit), peak is inflated before headroom.
3. Verdict
High-end GPUs ≥400 W get a warning to consider one tier higher for spikes. Otherwise the recommended size is shown as a comfortable 80 Plus Bronze-or-better floor. Full build advice: How to choose parts.