Published: July 25, 2019
Confused about graphics card compatibility and wondering what the different GPU slot types mean? You're not alone. First and foremost, you may wonder what "slots" means in regards to video cards, and it's a good question as it could refer to different things. A graphics card only needs to physically connect and plug into one PCIe slot on the motherboard (or PCI slot for older computers), but cards differ in how many PCIe slots they effectively take up (or block, to be more specific) on the motherboard because of the GPU cooler/fans sticking out over adjacent PCIe slots.
Furthermore, cards also differ in how many rear expansion slots they will need available in the back of your case as well, which are the metal brackets that you remove when installing a card (so that the I/O connections such as HDMI/DisplayPort/DVI can stick out the back of your computer as they should).
But here's where it can get confusing: sometimes a GPU will have different requirements in terms of how many PCIe slots and how many case expansion slots they will need available. For example, a certain card might take up 2 expansion slots in the back of your case (metal brackets), but might actually take up more than 2 PCIe slots on your motherboard (in this case it could be a 2.5 or 2.7 slot GPU - more on that later).
Cards come in all shapes and sizes, and could actually be a 1 slot, 1.5 slot, 2 slot, 2.5 slot, 2.7/2.75 slot, or 3 slot graphics card (phew). But what do all of these GPU slot sizes mean in terms of compatibility with your motherboard and case? More specifically, how many PCIe slots and case expansion slots will you need for each type? Let's break it all down so you can confidently choose the right graphics card that's compatible with your PC build and avoid potential space/clearance issues.
A single slot GPU is the most compact of all GPU slot sizes and takes up the least amount of space in your case and on your motherboard. But what are the actual requirements for a single slot graphics card? In this instance it's simple, as a single slot GPU needs both 1 PCIe slot available on the motherboard, and also 1 rear expansion slot in your case. Because they are thin, they won't cause space issues on a near PCIe port.
The EVGA GT 1030 SC Single Slot Graphics Card is an example of a modern single slot GPU on the market, and with this particular GPU it actually has "single slot" in its actual model name. But most cards won't, and so to find out the slot type of a card you'll need to have a look around the product listing, or better yet check the manufacturer's website for the official specs and it should be listed there. Also keep in mind the spec could be listed differently from card to card so look for a spec called slots/width/height/thickness (it can technically be referred to as width OR height because it depends what angle you're looking at your build from ;p).
A GPU that's listed as having 1.5 slots will only take up 1 rear expansion slot on the back of your case, just like a card that's listed as having 1 slot, but its size/width is a bit bigger than a single slot GPU and therefore you will need a bit of clearance directly below the card. In other words, a 1.5 slot graphics card could use up a bit of the PCIe slot directly under the one you plug your card into.
When the manufacturer lists a card as having 1.5 slots, it's not an exact measurement, but a heads-up that you could have clearance issues if you want to install another PCIe card right next to your graphics card (it may or may not fit depending on the size of that additional card). An example of a current 1.5 slot GPU is the EVGA GeForce GT 1030 SC 2GB GDDR5 Low Profile Graphic Card, which will fit in 1 slot (1 PCIe slot and 1 case expansion bracket) but will hover over the adjacent slot:
If a single slot GPU takes up one expansion slot in your case (and only uses up one PCIe slot on the motherboard), and a 1.5 slot GPU also takes up one expansion slot in your case (yet will use up some of the PCIe slot right under/next to it), then you should know what a dual slot GPU means. Yup, a dual slot graphics card will take up 2 expansion slots in your case, and 2 whole PCIe slots on your motherboard (though of course still only plugging into one PCIe port).
Dual slot GPUs are perhaps the most common these days, as most cooling solutions on modern GPUs take up a bit of space (and being installed in 2 rear case slots instead of 1 is more secure and stable). A picture is worth a wall of text though, so if you're still confused as to what a dual slot graphics card means then enter my old dual-slot Gigabyte GTX 1050 Ti below: (which as you can see takes up 2 case slots and 2 motherboard slots)
Now we start getting into the larger/wider models, and if you've read until now you should already know what a 2.5 slot GPU means. Like a standard dual-slot GPU, a 2.5 slot graphics card will require 2 free expansion slots in the rear of your case, however it will also fully cover 2 PCIe slots on your motherboard - and then some. It won't fully cover 3 slots like a triple-slot card would, but it may or may not render that third PCIe slot unusable (the one directly next to/under the 2nd slot). As you can see in the photo below of a typical 2.5 slot graphics card, the width/height (depends on the angle you're looking from) extends a bit further than the 2 metal slots due to the cooling/fans of the card.
A 2.5 slot GPU would only be a problem if your graphics card is sitting over the 2 bottom slots on your motherboard (and you have no further room whatsoever below that 2nd and last slot, ie your card would touch the case/bottom-mounted PSU etc), or if you were planning on using that third slot for another add-on PCI/PCIe card such as an extra GPU for SLI/CrossFire, a WiFi desktop network adapter, or a sound card. The MSI GeForce RTX 2060 6GB Gaming Z is an example of a modern 2.5 slot GPU, which like standard dual-slot GPUs are quite common:
Then there's also 2.7 slot GPUs out there in the wilderness, which may be officially listed as 2.75 slots instead in the specs, but they're essentially the same thing as GPU slots aren't official measurements by the manufacturer and only an estimation (there is no specific, universal slot size/width/height). As you can imagine, 2.7 and 2.75 slot GPUs are slightly wider/taller than 2.5 slot models, with a modern example being the EVGA GeForce RTX 2080 Ti FTW3 Ultra Gaming Graphics Card which isn't something you want to be going anywhere near if rocking a small form-factor case and/or motherboard:
Yup - it's getting a bit ridiculous now, but don't worry as we're at the last GPU slot type. Although, believe it or not, technically there was actually a frightening 4-slot monster released a few years ago, but you're never going to see that on a modern card (let alone a true 3 slot one). You know the deal by now; a triple slot GPU will need 3 rear I/O expansion slots in your case, and will fully cover/hover/block/dominate/lol over an entire full 3 PCIe slots.
These things are super-wide beasts as you can imagine, taking up a wide area in your system (though 2.7 slot GPUs are not far behind in terms of size), but they are quite rare and I can't think of any recently-released triple-slot cards on the market right now (though there are plenty of 2.7/2.75 slot models). There's just no need or real-world advantage of 3 slot cards, even with high-end high-powered GPUs, hence why we don't see them often (and they now seem to only be a thing of the past). Here's a side shot of what a true triple slot graphics card would look like: (the old ASUS GeForce GTX 570 Fermi for anyone wondering)
When it comes to GPU slots, keep in mind they're an informal measurement. In other words, a 1.5 or 2.5 slot card doesn't take up exactly 1.5 or 2.5 slots, and whether or not you'll have clearance issues will depend on your specific combination of case, motherboard, graphics card/s, other PCI/PCIe cards, etc.
But the most important thing to account for when checking if your graphics card will be compatible with your PC build is ensure you have enough slots for that GPU - and that means having both enough free expansion slots in the rear of your case (case specs should list this under "expansion slots", but for most builds you should have plenty unless you're using a very small case), as well as ensuring you have enough physical PCIe slots on your motherboard for both your graphics card and any other PCIe cards you'll be using.
If you're doing SLI/CrossFire with multiple GPUs, you'll need to plan your slots more carefully. For example, if you're using two 2.5/2.7 slot GPUs, you will need 2 empty PCIe slots in-between the two PCIe slots you'll be connecting your GPUs in (so a minimum total of 6 available PCIe slots).
Hope this guide helped you understand what the different GPU slot types mean, and if you have a question, or you're a fellow enthusiast who has something to add to this guide (perhaps we missed an important detail that would help beginners, or you think we could explain something a bit more clearly), we'd love to hear from you.
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Anyway, hope this guide helped and good luck with your build or upgrade!