Pick your parts and this tool works out the wattage your build actually needs, based on real peak draw rather than the inflated figure a card maker quotes. It also tells you the minimum that will work, so you can see how much headroom you are paying for.
Why our number is usually lower than the one on the box
Graphics card and motherboard makers quote a system wattage that assumes the worst: a cheap supply whose rating is overstated, an overclocked processor, and a full complement of drives and fans. That is a sensible default for a company that does not know what you own, but it routinely sends people to a unit 200 W larger than their build will ever draw.
We size from the components you actually selected. On a reputable 80 Plus unit, our figure is the one that applies. If you are reusing an old or unbranded supply, take the next size up instead.
Why we size at about 75% load
A power supply is most efficient, and quietest, somewhere around half to three quarters of its rating. Sizing at roughly 75% peak load keeps you in that band, leaves room for one graphics card upgrade later, and avoids the fan ramping every time a scene gets heavy. Sizing at the absolute minimum works, but the unit will run hot and loud at exactly the moments you would rather it did not.
Transient spikes and ATX 3.1
Modern high end cards draw very brief spikes far above their rated power, sometimes approaching double it for a fraction of a millisecond. An older ATX 2.x supply can read that as a fault and shut down, which looks exactly like a random crash in a game and sends people hunting for driver problems that do not exist.
ATX 3.0 and 3.1 units are specified to ride those spikes out. If your card is rated at 250 W or more, the specification matters more than the wattage. Where that applies the calculator says so on the result.
The 12V-2×6 connector
Cards that use the 12-pin power connector should be fed with the native cable that came with the supply, not an adapter chained from older connectors. Seat it until it clicks. The reported failures of this connector have overwhelmingly involved partially seated plugs and adapters, not the connector itself at rest.
What efficiency ratings mean for you
- 80 Plus Bronze is the sensible floor for a gaming build.
- Gold is the value sweet spot, and usually quieter under load.
- Platinum and Titanium save a few watts you will not notice on a power bill. Buy them for the build quality and warranty, not the efficiency.
- The rating describes efficiency, not safety or quality. A well reviewed Bronze unit beats a poorly made Gold one every time.
Can a weak power supply cause crashes?
Yes, and it is one of the most commonly misdiagnosed faults in PC building. A supply that cannot hold up under load produces sudden restarts or black screens during demanding scenes, with no error message and nothing in the logs. If a system is stable at the desktop but drops out in games, the supply is worth ruling out before anything else.