Guide

Why brand PSU calculators overestimate

Cooler Master, Seasonic, be quiet!, and MSI publish wattage tools next to the power supplies they sell. pc-builds.com wraps a similar adder in ads. They are useful as a reminder that a PC is more than a GPU. They are a poor place to learn the smallest honest size, because the incentive points up the wattage chart.

The pattern

A typical brand tool takes a CPU's highest power limit, adds a GPU's full board power, adds a flat platform number, adds a headroom percentage, and rounds up to a unit in that brand's catalog. Each step can be defended alone. Stacked, they stop being an estimate and become a recommendation to buy the next chassis up.

The CPU step is the expensive one. Intel's Maximum Turbo Power and AMD's PPT are all-core limits. A Core i9-14900K is 125 W base and 253 W maximum turbo. In a GPU-bound game the package is often nearer the base than the turbo limit, because the cores are not all saturated the way a renderer saturates them. Using 253 W for a gaming PC, then adding a 100% GPU, describes a workload that rarely happens: a full CPU stress test and a full GPU stress test at once. WattWise shows that workload as the power-limit ceiling, and it shows gaming as the base-power plan. They are different sentences.

The GPU step has the opposite problem. Vendors rarely publish an in-game average. Some cards sit on their power limit in demanding games; some do not. Inventing "this card games at 72% of TGP" would be a fabricated measurement. WattWise uses the rating and says so. The padding we refuse is the extra percentage after that rating, and the silent substitution of a CPU turbo limit into a gaming total.

The gap people measured

Builders comparing brand calculators with a wall meter have reported the tool running hot, on the order of about 97 W above the measured system in at least one public comparison. WattWise does not treat that anecdote as a calibration constant. It is the reason the two profiles exist. If your wall meter says 420 W while the ceiling says 560 W, the meter is the gaming reality and the ceiling is the overlap case. A calculator that only prints 750 W has hidden the difference you needed.

OuterVision's long-running calculator, including its expert mode for efficiency payback and per-part overclocks, went offline in 2025. Newer sites have not all brought those pieces back. The payback tool and the offset sliders on WattWise are there because those questions are still real, and they should not require a brand's storefront.

What "neutral" commits us to

• No shelf prices, no featured unit, no "recommended PSU" that is a product.
• Shop links open a store search for a wattage class. The disclaimer covers commissions and the limit of a result.
• Vendor system minimums are quoted with the reference CPU, not blended into our minimum.
• Spikes stay in the connector spec.
• If a figure is derived or only reported by reviewers, the CPU table says derived or reported. The Ryzen 9 9950X is the clearest case: AMD prints 170 W TDP, and the stock 200 W PPT is documented by reviewers rather than on the product page.

A neutral number can still be wrong. Allowances for the motherboard, fans, and drives are planning figures, and they are labeled that way. Expert mode exists so you can count the parts you actually installed. If you own a wall meter, believe the meter.

Start with the calculator, then read a GPU guide for the card you are buying. The methodology has the formulas.