PC Power Supply (PSU) Calculator

About the PC Power Supply (PSU) Calculator

Pick your processor and graphics card (or type their power ratings), add drives, fans and the rest, and the calculator recommends a power-supply size, an efficiency tier and the cables to look for. The presets carry the figures the makers publish: Intel’s Maximum Turbo Power, AMD’s Default TDP, NVIDIA’s Total Graphics Power and AMD’s Typical Board Power, with each card maker’s own minimum PSU.

A graphics card does not draw a steady load: for fractions of a second it can pull far more than its rating. The sizing follows Intel’s ATX Version 3 power supply design guide, which quotes the PCIe limits for those spikes (up to 3× the card’s rating for 100 µs) and says how far an ATX 3 power supply must ride through them (200% of its rating for 100 µs, 120% for 100 ms). The calculator shows every step, so you can see whether the sustained load or a spike sets the size, and what each 80 PLUS tier would cost you to run.

Without a pass, the free preview shows the recommended power supply size in full, with the reasons for it and the first rows of each table; a Pro pass unlocks the sustained load, the minimum and the peak, the whole tables and Copy summary.

Common uses

• Choosing a power supply for a new PC build, or checking that an upgrade (a bigger graphics card) still fits.
• Deciding between an ATX 3 power supply with a 12V-2x6 cable and an older one with 8-pin plugs.
• Comparing what Bronze, Gold and Platinum efficiency would cost you to run.
• Finding the wall draw of a PC before sizing a UPS or an inverter.

How the size is worked out

• Sustained load = processor + 15% for its power delivery + graphics cards + everything else. Intel’s design guide budgets 26 A at 11.2 V (about 291 W) for its 125 W-class processors, whose Maximum Turbo Power is up to 253 W, so the calculator adds 15% of the processor figure for the motherboard’s voltage regulators (processor configurations).
• Graphics spikes: over an interval T a card may average up to R × its sustained rating, R = 3 up to 100 µs and 4 − 0.2171 × ln(T in µs) up to one second: 2.5 at 1 ms, 2.0 at 10 ms and 1.5 at 100 ms (PCIe add-in card power excursions).
• Minimum PSU = the largest of the sustained load and each spike (graphics spike + the rest of the PC) divided by the power supply’s allowance for that interval.
• Recommended = the minimum, or the sustained load plus your headroom if that is more, raised to the graphics card maker’s minimum if you ask, and rounded up to a common size (300 W to 1,600 W).

Brief spikes: what an ATX 3 power supply must ride through

The design guide (PSU power excursion) asks power supplies above 450 W that have a 12V-2x6 connector to deliver 200% of their rating for 100 µs, 180% for 1 ms, 160% for 10 ms and 120% for 100 ms; power supplies of 450 W or less and those without the 12V-2x6 connector 150%, 145%, 135% and 110%. Older ATX 2.x units have no such rating, so for them the calculator makes the 100 ms spike fit within the rating itself, which is the safe reading.

Intel’s own example budgets (power budgets) pair a 450 W card with a 300 W processor budget and 250 W for the rest of the platform in a 1,000 W supply, and a 600 W card with 300 W and 300 W in a 1,200 W one.

Power plugs and what they carry

By the PCIe CEM 5.1 limits in the guide (auxiliary power connectors), a graphics card may draw 75 W from its slot, 75 W through each 6-pin plug, 150 W through each 8-pin plug and up to 600 W through a 16-pin 12V-2x6 cable, whose two sense pins tell the card whether the cable is good for 150, 300, 450 or 600 W. 12V-2x6 is the updated name of the 12VHPWR connector: the guide changed the header’s pin lengths, and the cable plug stayed the same. Use the cables your power supply’s maker supplies for it.

Efficiency tiers (80 PLUS)

Each tier sets a minimum efficiency at 20%, 50% and 100% of the rated load (80 PLUS ratings). For 115 V internal power supplies: Bronze 82 / 85 / 82%, Silver 85 / 88 / 85%, Gold 87 / 90 / 87%, Platinum 90 / 92 / 89%, Titanium 92 / 94 / 90% (and 90% at 10%). For 230 V EU internal ones: Bronze 85 / 88 / 85%, Gold 90 / 92 / 89%, Platinum 92 / 94 / 90%, Titanium 93 / 95 / 91%. The table in the tool interpolates between those points at your load and turns the difference into watts, heat and energy a year.

The other parts

The defaults under Everything else are round starting figures, not measurements of your parts: change them to your spec sheets. A fan’s label gives its current (0.15 A × 12 V = 1.8 W); a USB 2.0 port supplies up to 2.5 W, a USB 3 port up to 4.5 W, and USB-C 7.5 W or 15 W at 5 V (USB power). Hard drives briefly draw more as they spin up: their spec sheets list the 12 V start-up current.

Limitations

• An estimate from the makers’ ratings and the formulas above, not a measurement: partner graphics cards with raised power limits draw more than the reference figure, and a plug-in power meter shows what your PC really takes.
• AMD’s product pages list only the Default TDP for its desktop processors; at stock settings they may draw more from the socket (up to their PPT limit), so enter the PPT for a closer figure.
• Several graphics cards: Intel’s guide sizes spikes for one card, and this calculator adds every card’s spike together.
• It does not judge a power supply’s build quality, protections, 12 V rail layout or cables; a well-made unit of the right size matters more than a bigger one.
• Not a professional electrical design; check the wall socket and wiring for very large systems.

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