How do you work out the PSU wattage your PC needs?
There are two ways: use the TweakFa PSU calculator above, or do the math yourself.
Around 90% of your PC’s power draw comes from two parts: the graphics card and the CPU. Fans, the CPU cooler, RAM, the motherboard and the rest draw very little next to them. Add them in the calculator and you’ll see the totals barely move.
To do it by hand, add up the worst-case power draw (TDP) of your graphics card and CPU, then allow roughly 50 to 200W for everything else. Where you land in that range depends on how many fans, drives, RAM sticks and how much case lighting you have.
Then add about 10 to 20% on top of that total, and you have a sensible size for your power supply. A PSU should always have 10 to 20% more capacity than your system’s peak draw. That helps both the PSU and your components in several ways, the biggest being that the PSU never runs flat out, so it runs cooler and lasts longer.
What’s the difference between peak and average power draw?
Peak power draw is what your system pulls at absolute full load: CPU, graphics card, RAM, fans, drives and every other part running at 100% at the same time and putting the most strain possible on the PSU. Getting a PC to that point, especially while gaming, is close to impossible, so in normal use your system never actually reaches its peak. Average power draw is what your system typically pulls under a real workload such as gaming or rendering.
Why not pick a PSU based on average draw?
Because a PSU has to be ready for anything your system might ask of it. If you size the PSU to your average draw and the graphics card or CPU hits a power spike, the PC can shut off without warning. That’s the last thing you want in the middle of a render, or even a game.
PSUs are also most stable at low load and least stable at high load. The closer you push a unit to its rated capacity, the less stable it gets: ripple and transient response, two of the key measures of PSU quality, both get worse at higher loads. If either gets bad enough, it can damage your components over time and even make your system unstable.
What does the “Future-proof” option mean?
It’s for anyone who wants room to upgrade later without replacing the PSU. It leaves about 30 to 40% of headroom, so you can move to a hungrier graphics card or CPU down the line and keep the same power supply.
Why does the USB 3.2 Gen 2 (100W) option add 100W?
On systems with a USB 3.2 Gen 2 port rated for 100W, that port can deliver up to 100W to charge or power other devices. If your PC has one and you use it for power-hungry jobs like charging a phone or laptop, turn this option on so it’s counted in your total.
My part isn’t on the list. What now?
Post the model in the comments on this page and our support team will add it to the calculator as soon as they can.
