About the PC Power Supply Calculator
This PC power supply calculator estimates how many watts your build draws at full load and recommends a standard PSU size with sensible headroom. Enter the CPU and graphics card power, the motherboard size, and how many RAM sticks, SSDs, hard drives and fans you have; the tool adds typical figures for each part and rounds the result up to the next common power supply rating (550 W, 650 W, 750 W, 850 W, 1000 W and so on).
It is for gamers and PC builders choosing a PSU for a new build or a GPU upgrade, and for anyone wondering whether their existing supply is big enough. A breakdown chart shows where the power goes, and the wall-draw and yearly cost figures help you compare efficiency ratings.
For the most accurate result, use the CPU’s maximum package power (PL2/PPT, which can be well above its advertised TDP) and the graphics card’s total board power from the manufacturer. Modern GPUs can produce brief power spikes far above their rating, which is why a 30–40% headroom margin is a good default. Component figures for RAM, drives and fans are typical estimates, not measurements.
With the default inputs, the recommended psu size is 750 W. Change any value above to recalculate instantly.
How to use the pc power supply calculator
- 1Enter your CPU’s maximum power and the graphics card’s board power.
- 2Pick the motherboard size and count your RAM sticks, drives and fans.
- 3Add any extras such as an AIO pump, RGB lighting or USB devices.
- 4Set a headroom margin (30–40% is typical) and toggle overclocking if needed.
- 5Buy a PSU at least as large as the recommendation, from a reputable brand.
Formula and method
The calculator adds the maximum power of each component. CPU and GPU figures are what you enter (multiplied by 1.2 if you overclock); the rest use typical estimates: about 30–80 W for the motherboard and chipset depending on size, 5 W per RAM module, 5 W per SSD, 9 W per active 3.5-inch hard drive and 3 W per fan. The total is the DC load the power supply must deliver.
That load is increased by the headroom margin and rounded up to the next standard PSU size. Wall draw divides the DC load by the PSU efficiency, since a supply that is 90% efficient pulls about 11% more from the outlet than it delivers. Yearly cost = wall watts × hours per day × 365 ÷ 1,000 × price per kWh.
- Load
- Estimated full-load DC power (W)
- n
- Number of graphics cards
- headroom
- Safety margin as a fraction
- efficiency
- PSU efficiency at that load (fraction)
Worked examples
Mid-range gaming PC: 125 W CPU, 285 W GPU
CPU 125 + GPU 285 + ATX board 50 + 2 RAM (10) + 2 SSDs (10) + 4 fans (12) + 20 W extras = 512 W. Adding 30% gives 665.6 W, so the next standard size is 750 W. At 90% efficiency it pulls about 569 W from the wall, costing about $141 a year for 4 hours a day at $0.17/kWh.
Overclocked high-end build: 170 W CPU, 450 W GPU
Overclocking adds 20%: CPU 204 W and GPU 540 W. With an 80 W E-ATX board, 4 RAM (20), 3 SSDs (15), 2 HDDs (18), 6 fans (18) and 20 W extras, the load is 915 W. With 30% headroom that is 1,189.5 W, so choose a 1,200 W PSU.
Office PC with integrated graphics
A 65 W CPU, micro-ATX board (40), two RAM sticks (10), one SSD (5), two fans (6) and 10 W extras total 136 W. Even with headroom (177 W) the smallest common size, 450 W, is plenty. At 85% efficiency it draws 160 W, about $79 a year for 8 hours a day.
Frequently asked questions
How many watts does my PC need?+
Add the CPU’s maximum power, the GPU’s board power and roughly 80–130 W for the motherboard, memory, drives and fans, then add 30–40% headroom. A typical gaming PC with a 125 W CPU and a 285 W GPU needs about a 750 W PSU.
Is a bigger power supply bad?+
No — a PSU only delivers the power the components ask for, so an oversized unit does not waste much energy. Very oversized units can be slightly less efficient at light loads and cost more, so aim for full load around 50–80% of the rating.
Should I use CPU TDP or maximum power?+
Use maximum package power (Intel PL2, AMD PPT) when you know it. Many desktop CPUs with a 65 W or 125 W TDP can draw 90–250 W under heavy boost, which TDP alone understates.
Why do graphics cards need so much headroom?+
Modern GPUs can draw brief transient spikes well above their rated board power for milliseconds. A PSU with too little margin may trip its over-current protection and shut the PC down even though average power seems fine.
Does 80 PLUS Gold mean the PSU is more powerful?+
No. 80 PLUS ratings measure efficiency, not output. A Gold unit wastes less power as heat (about 90% efficient near half load) than a Bronze unit (about 85%), which lowers electricity cost and noise.