Do you know how much watt your computer draws? The answer is probably no. You are even less likely to know the power draw of a pc that has yet to be build. Therefore choosing the correct power supply unit can be tricky. Luckily there are serveral methods to determine the minim required power supply.

Required PSU Method 1: PcInside’s Rules of Thumb

PcInside has created a rule of thumb that allows you to easily choose the right power supply. It is based on the fact that a modern cpu seldomly draws more than 100W. Components such as hard disks, SSD’s and fans have no significant power draw. Nowadays the most power hungry component is your graphics card. Therefore this component will be the primary decision maker for our rules of thumb.

No dedicated graphics card: 300W

A power supply of 300W will be fine if for any pc as long as you do not have a dedicated graphics card installed. This is basically the smallest PSU you can find, with the exception of the picoPSU’s.

$100 Graphics card: 400W

Affordable graphics cards usually draw up to 75W directly through the motherboard. If there is an additional 6-pin power connecter than they can draw up to 150W. To be safe I recommend getting a 400W PSU.

$200 – $350 Graphics card: 500W

Serious graphics card require serious power. Often they require 2x 6 pins  power connectors (150W maximum) or even 2x 8 pins (300W maximum). A 500W power supply is strongly recommended in this scenario.

$350+ Graphics card: 800W

Currently the most power hungry graphics card have a TDP of 250W, with a peak power draw of 282W. It only makes sense to purchase these bad boys when you overclock your cpu, which will draw at least 150W in that state. Therefore the peak of total power drawn will be about 450W. This makes a 500W power supply the bare minimum requirement. It will definitely work but there is not much room left.

However why would you settle for the bare minimum? It makes more sense to get a bigger power supply with a capacity of about two times the average load (2x 400W=800W).  This will have a few benefits.

Multiple graphics cards

If you will be using two or more graphics cards then a 750W or bigger power supply unit is recommended.

Note: If you plan to combine multiple graphics card that are cheaper then $300 then you should NOT be doing this!. Check out the following article: SLI en Crossfire is het combineren van meerdere grafische kaarten – zo werkt het (will be translated soon) to find out how and why. You are always better off with the single fastest graphics card.

Required PSU Method 2: Calculators

There are a lot of websites out there that will estimate your power requirements based on your components. Although not all of them are spot on, the following website will assist you in in figuring out what power supply to get:

Required PSU Method 3: Use the official requirements form the graphics card

If the previous methods require too much information from you then there is a simpler method. When you purchase a decent graphics card you can always ask for the minimum requirements for that specific component. These minimum requirements can also be found on the website of the appropriate manufactorer. AMD (Ati Radeon) even has a list of approved power supply units from various brands.

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Founder of PcInside. Studied Business Administration (MSc) but always found computer hardware just as interesting.