If you want more performance so you can play the latest games at high resolutions and maximum quality, you need a decent graphics card. Here we explain how to know if a graphics card will fit in your PC and if it will be compatible.

It's crucial to get this stage right, as without it you'll be left with a powerful graphics card that doesn't work properly with your PC. In this article, we'll show you how to make sure a graphics card is both compatible with your device and will physically fit inside your case. 

Once that's sorted, the process of actually installing it is relatively simple by comparison. 

See also: How to add a graphics card to your laptop

A background to PC graphics

Many PCs rely on so-called ‘integrated’ graphics which is either a chip on the motherboard or one built into the CPU itself. Other PCs have a ‘dedicated’ graphics card, which plugs into an expansion slot on the motherboard.

You can usually tell which type your PC uses by the location of the port you use to connect your monitor. If it’s in among the other ports, such as USB and Ethernet, then it’s integrated graphics. If the port is separate to the others, and there’s more than one port, such as a pair of DVI outputs, HDMI or DisplayPort, it’s probably a dedicated graphics card.

Whichever type it is, you’ll need both an expansion slot – called PCI Express – and a corresponding slot in the case – with a removable backplate where the connections will sit in order to fit a dedicated graphics card.

How to know if a graphics card is compatible: Find the PCI Express slot

On many PCs, there will be a few expansion slots on the motherboard. Typically they will all be PCI Express, but for a graphics card you need a PCI Express x16 slot. There are three versions of this slot, but they’re backwards compatible, so a modern PCI Express 3.0 graphics card will work in a motherboard with a PCI Express x16 2.0 slot.

This motherboard has two PCI Express x16 slots. It's most common to use the upper-most one for a graphics card, but if you're fitting two cards in an nVidia SLI or AMD Crossfire setup, you'll need both. Check which standard your motherboard supports before investing in a pair of cards, though.

How to know if a graphics card is compatible

How to know if a graphics card is compatible: length and height

More powerful graphics cards tend to have large fans to keep them cool, and this makes them twice as thick as a ‘single-height’ card. The way most PCs are built means that the fan assembly will be underneath the card rather than on top of it, so you’ll need an unused slot – and backplate – directly underneath the PCI Express x16 slot.

Plus, you need to measure the distance from the backplate to any components which would block a long graphics card at the front of your case. Don’t forget that some cards have their power sockets on their back edge rather than the side, so you’ll need to add about 30-40mm to the length of your chosen card to guarantee it will fit.

If you’re unsure how long a card is, ask the manufacturer, seller or try our own forums to find someone who owns that card already and can confirm how big it is.

How to know if a graphics card is compatible: power requirements

Even if you have PCI Express x16 slot and plenty of room, you’ll need extra power for most graphics cards. Your power supply is likely to have PCI-E power connectors, but they may be bundled up and tied out of the way if no graphics card is currently fitted.

These connectors are usually black, marked as PCI-E and have six pins in a 3x2 arrangement.

If your PSU doesn’t have these, you can buy adaptors which connect to the standard four-pin power or SATA connectors. Be careful with graphics cards that require two PCI Express power connectors as each of these should be connected to a different 12v rail of the power supply. On most PSUs this means connecting each of the two adaptors to a different ‘daisy chain’ of power connectors, and not to the same chain.

How to know if a graphics card is compatible

Finally, make sure your power supply has enough headroom above what the existing components are drawing to power your new graphics card.

It can be tricky to work out if yours does, but a good rule of thumb is that high-end graphics cards will require at least a 600W PSU, if not more. It’s wrong to assume that a PSU can output its maximum power rating continuously, and you’re sure to run into problems if your components are drawing more than around 80 percent of the PSU’s top rating.

Again, it’s fairly easy to check how much power a graphics card draws from its specifications by searching online.

Considering a purchase? Check out our round-up of the best graphics cards

To ensure you get the best price, it's also worth checking out the best graphics card deals