Computer PSU Wattage Calculator: Estimate Power Needs

Power supply sizes for popular builds

Each row has an ATX board, two memory sticks, one NVMe drive, three case fans and an air cooler. Pick your own parts above for exact numbers.

Builds with a power-hungry processor land above the maker's figure, since the calculator keeps 20% spare at full load. NVIDIA's 1,000 W for the RTX 5090 is a minimum, based on a PC with a Ryzen 9 9950X.

How the calculator works

It adds up what every part can draw at its limit, all at the same time. That's your full load, the most the PC should ever ask of its power supply.

Graphics cards count at their total board power from NVIDIA, AMD and Intel. Intel processors count at the Maximum Turbo Power on Intel's spec pages.

Ryzen chips count at AMD's Package Power Tracking (PPT) limit, which AMD sets at 1.35 times the TDP. So a Ryzen 7 9800X3D, sold as a 120 W chip, counts as 162 W.

Older Intel chips count at their turbo limit, called PL2, from Intel's datasheets. A Core i9-10900K is sold as a 125 W chip, but its PL2 is 250 W.

The rest of the PC gets set amounts: 35 to 80 W for the motherboard, 5 W per memory stick, 7 W per NVMe drive, 10 W per hard drive, 3 W per fan and 10 W for your keyboard, mouse and other USB basics.

Why it leaves 20% spare

The calculator picks the smallest common size that keeps the full load at or under 80% of the rating. That's the top of the range where power supplies run most efficiently, says be quiet!, which is 50% to 80%.

Graphics cards also jump past their rating for a split second. TechPowerUp caught an RTX 5090 at 644 W in short bursts, against its 575 W rating. The spare room soaks up those spikes and leaves space for a faster card later.

It also never suggests less than the card's maker asks for. NVIDIA lists 550 W for the RTX 5060, and AMD lists 750 W for the RX 9070 XT.

Is your power supply big enough?

Choose Check my PSU above and type the wattage from the label on its side. You'll see how hard your build works it, and the size to buy if it's too small.

A PC that shuts off or restarts in games, but runs fine on the desktop, is the classic sign of a weak or worn power supply. Our free PC Reporter logs every sudden restart, so you can see if they line up with gaming.

The warranty hints at how long a good unit should last. Corsair backs its RM850x for 10 years and Seasonic its PRIME TX for 12. If yours is past its warranty, plan to replace it with your next big upgrade.

What it costs to run

The running cost uses your gaming draw. That's the graphics card flat out, plus the processor at 60% of its limit, near the top of TechPowerUp's game tests.

It also adds the power supply's own losses, since an 80 PLUS Gold unit only has to be 87% efficient at full load. Games with a frame rate cap use less, so treat the cost as a high estimate.

For the price, use the rate on your power bill. The U.S. average for homes was 18.31 cents per kWh in July 2026, says the U.S. Energy Information Administration, which also lists each state.

What to look for when you buy

An ATX 3.1 unit

Intel's ATX 3 design guide asks units over 450 W to handle twice their rating for 100 microseconds. That's what lets them ride out graphics card spikes without shutting off.

The right graphics card cables

The RTX 50 Founders Edition cards use one 16-pin power plug, the newer 12V-2x6 version, as Tom's Hardware notes. Most ATX 3.1 units include a matching cable. Other cards use 8-pin plugs, like the two on AMD's RX 9070 XT.

Plugs can differ between versions of the same card, as NVIDIA points out in its RTX 4060 guide and Intel in its Arc setup guide. Check the exact card's spec page against the power supply's cable list.

Efficiency and fit

The 80 PLUS program tests how much power a unit wastes as heat, from Bronze up to Titanium. Gold is a good middle ground for most builds.

Most cases take a standard ATX power supply, but small ones may need the shorter SFX size. Check your case manual before you order.

Plan the rest of your build

• See if your CPU cooler and case fans can carry all that heat with the cooling calculator.
• Test your fan layout against all that heat in the PC Airflow Simulator.
• Keep the PC running through outages with the gaming PC UPS calculator.
• See if your processor holds back a new card with the bottleneck calculator.
• Find your best next part, and whether it fits, with the upgrade checker.
• Check which games your parts can run with the system requirements checker.
• Learn what each part does in our guide to computer parts.
• Browse all our free PC tools.