Power Supply Calculator
Estimate your PC's total power draw by listing components and their wattage, then get a recommended PSU size with headroom.
Choosing the right power supply unit (PSU) for a PC build or electronics project requires calculating the total power draw of all components plus a headroom buffer. An undersized PSU causes system instability, crashes, or permanent damage. An oversized PSU is wasteful and unnecessary.
Total System Wattage formula:
Total Draw = CPU TDP + GPU TDP + RAM Wattage + Storage Wattage + Peripherals + Motherboard
Recommended PSU Wattage:
PSU Wattage = Total Draw / 0.80
The division by 0.80 keeps the PSU operating at 80% load maximum — the most efficient and safest operating point.
What each variable means:
- TDP (Thermal Design Power) — the maximum sustained power draw of a CPU or GPU (watts); listed on manufacturer spec sheets; represents real-world peak gaming/rendering load
- RAM — DDR4/DDR5 sticks draw ~2–5 W each; 4 sticks = 8–20 W total
- Storage — SATA SSD: ~2–4 W; NVMe SSD: ~5–10 W; HDD: ~6–10 W spinning + 2 W idle
- Motherboard — typically 30–80 W depending on VRM quality and features
- 80% rule — running a PSU at 80% rated load keeps temperatures manageable, reduces wear, and ensures peak transient loads (GPU spikes) are covered
Worked example — High-end gaming PC:
- CPU (Intel Core i9-14900K): 125 W TDP (boosting to 253 W)
- GPU (NVIDIA RTX 4080): 320 W TDP
- RAM (32 GB DDR5): 15 W
- NVMe SSDs (× 2): 15 W
- Motherboard: 50 W
- Cooling + fans + RGB: 20 W Total Draw: 545 W (at spec TDP) or up to 673 W at peak boost
PSU at 80% load: 673 / 0.80 = 841 W minimum → choose an 850 W or 1000 W 80 Plus Gold or better PSU.
80 Plus efficiency ratings: 80 Plus Bronze: 82–85% efficient | Gold: 87–90% | Platinum: 90–92% | Titanium: 92–96% Higher efficiency = less heat and lower electricity cost over years of operation.