PC Power Supply Calculator
Choose your processor and graphics card class, add memory, drives, fans and any overclock, and get your PC's estimated peak power draw and a recommended power supply size with sensible headroom. It also shows what the PC costs to run and how much a more efficient 80 PLUS rating saves.
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Use the maximum turbo / PPT power from the spec sheet
Total board power (TBP/TGP) from the card's spec page
About 4 W per DDR4/DDR5 module
LED strips, USB-powered gear, capture or sound cards
Gaming ≈ 50–70%, office/web ≈ 15–25%, rendering ≈ 90%
How to use the PC Power Supply Calculator
- Pick the CPU and GPU class, or choose Custom and type the wattage from the spec sheet.
- Add memory, drives and cooling: RAM sticks, SSDs, hard drives, fans and an AIO pump.
- Set overclocking and headroom; 70% peak load is a good default.
- Enter your usage and electricity price to see running costs.
- Read the recommended PSU and compare efficiency ratings in the table.
How the PSU size is worked out
The calculator adds the peak (worst-case) draw of every component, then divides by the share of capacity you want to use at peak:
Recommended PSU = total peak load ÷ target load fraction, rounded up to the next common size (450, 550, 650, 750, 850, 1000, 1200 W…).
Example: a performance CPU (200 W), an upper mid-range GPU (250 W), an ATX board (50 W), 2 RAM sticks (8 W), an NVMe SSD (7 W), a hard drive (9 W), 4 fans (12 W) and 15 W of RGB and USB add up to 551 W. At a 70% target, 551 ÷ 0.7 = 787 W, so an 850 W unit is the recommendation.
Typical component power draw
| Component | Typical peak draw used here | Notes |
|---|---|---|
| CPU | 90–350 W by class | Use the maximum turbo/package power limit, not just the TDP, which is often lower than the real peak. |
| Graphics card | 75–575 W by class | Total board power from the spec page. Slot-powered cards are limited to 75 W. |
| Motherboard | 35–75 W | Chipset, VRM losses, onboard audio, networking and USB controllers. |
| RAM | ≈4 W per stick | DDR5 modules include their own voltage regulator. |
| NVMe SSD | ≈7 W | Fast PCIe 4.0/5.0 drives can peak higher during long writes. |
| SATA SSD | ≈4 W | |
| 3.5" hard drive | ≈9 W | Each drive can briefly draw 20 W or more from the 12 V rail while spinning up. |
| Case fan / AIO pump | ≈3 W / ≈8 W | Large RGB fans and high-speed fans draw more. |
Choosing a good power supply
- Follow the GPU maker's recommendation if it is higher than the result here; it accounts for that card's spikes and for lower-quality units.
- Check the connectors: enough 8-pin PCIe or a native 12V-2x6 cable for your graphics card, and the CPU EPS 8-pin connectors your board needs.
- Quality matters more than the label wattage. Look for independent reviews, protections (OCP, OVP, OPP, SCP, OTP) and a long warranty.
- Leave room to upgrade. If you plan a bigger graphics card later, size for it now; replacing a PSU means re-cabling the whole PC.
- Measure if you can. A plug-in power meter at the wall shows real draw; multiply it by the PSU efficiency to get the DC load.
Frequently asked questions
How many watts does my PC need?
Add up the peak power of every part: the CPU and graphics card make up most of it, then about 35–75 W for the motherboard, around 4 W per RAM stick, 4–9 W per drive and about 3 W per fan. A typical mid-range gaming PC peaks around 350–450 W; a high-end one with a 300 W+ graphics card can reach 550–700 W.
How much headroom should a power supply have?
Aim for your peak load to be about 60–70% of the PSU's rated wattage. That leaves room for brief power spikes, ageing capacitors and future upgrades, keeps the fan quieter, and keeps typical use near the 50% load point where units are most efficient.
Is a bigger power supply bad?
A PC only draws the power it needs, so a larger PSU does not waste much by itself. But a heavily oversized unit spends most of its time at very low load, where efficiency is lower, and it costs more to buy. Sizing so that peak load is 60–70% of capacity is a good balance.
What do 80 PLUS Bronze, Gold and Platinum mean?
They are efficiency certifications measured at 20%, 50% and 100% load. On 115 V, Bronze requires 82/85/82%, Silver 85/88/85%, Gold 87/90/87%, Platinum 90/92/89% and Titanium 92/94/90% (plus 90% at 10% load). Higher efficiency means less electricity turned into heat.
Is an 80 PLUS Gold PSU worth it?
It depends on how much you use the PC and what you pay for power. The comparison table shows the yearly saving versus a basic unit at your usage; for a few hours of gaming a day the difference between Bronze and Gold is usually a few dollars a year, while for an always-on or heavy-use PC it adds up faster. Gold units often also have better components and warranties.
Why do new graphics cards need a bigger PSU?
Modern high-end GPUs can draw short power spikes well above their rated board power. Older power supplies may shut down when that happens. The ATX 3.0/3.1 standard requires PSUs to tolerate these excursions, so for cards around 300 W and above an ATX 3.x unit with a native 12V-2x6 (12VHPWR) cable is a good choice, sized as the GPU maker recommends.
Are these wattages exact?
No. The classes use typical peak figures, and real draw depends on the exact models, BIOS power limits and workload. For a precise figure, select Custom and enter the CPU's maximum turbo power and the GPU's total board power from their spec pages, or measure your PC at the wall with a plug-in power meter.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.