Putting together a computer is a special experience that every geek needs to do at some point in their career. Underloved and overlooked, the decision of which case to choose is such a fundamentally important choice that I absolutely cannot stress enough that a good one will last you 10 years or more.

Today therefore, we present a mini-guide to choosing exactly the right case. Don't forget our free PDF guide to building your own PC, as well as Matt's advice on choosing the best parts.

Motherboard Form Factors

Whether you’re choosing a case to suit a motherboard or planning on finding a motherboard to suit that designer case, the form factor is the primary consideration. The main motherboard form factors in use today are as follows (from Wikipedia):

buying a pc case

They get smaller, but these aren’t in common use; another is Mini-ATX (not pictured).

Generally speaking, a Micro/Mini-ATX motherboard or a Mini-ITX will fit just fine into a full size ATX case, but always check the compatiblity listing. The only real difference between ATX form factors is the number of expansion and memory slots included; otherwise there’s little or no performance gain. If you’re looking to build an extreme gaming rig with multiple video cards then you’ll be looking to a full ATX motherboard capable case; for a smaller footprint the Micro-ATX standard is sufficient for most.

Mini-ITX is typically only used in very small media center or home-theatre systems. In this case, you’re probably working to fit your HTPC into a TV stand, so obviously your choice of case will be limited primarily by size.

Case Types

Apart from the form factor of the motherboard, you may also have a specific type of case in mind for a particular function. Let’s look at these briefly:

Full Tower / Server: These are great behemoths with space for typically up to 10 hard drives or multiple physical media devices (DVD duplication roles, for instance).

Desktop / Mini Tower: In a range of sizes come the standard desktop and mini/midi-towers that most users are familiar with. Check carefully, as these can usually take a full ATX motherboard but sometimes only a smaller form factor.

Rackmount: Measured in standard rack unit heights, rackmount cases come in variety of heights from slimline 1U to full height 4U, but you’d have trouble fitting a typical desktop CPU fan into a 1U (1.75") case. If you need a full PC to be ruggedized for concert touring, rackmount one into a flightcase; otherwise these are reserved for server rooms, and tragic geeks like myself who are turned on by rackmounted equipment.

buying a new pc case

HTPC: These cases are designed to match other components in your home theatre setup - perhaps with some nice blue LEDs on the front, rounded feet - it’s all about style. Sizes vary; you can get large HTPC cases that take full ATX, while some will only fit Mini-ITX.

buying a new pc case

Drive Bays

Every case will list the maximum number of 3.5" and 5" drive bays they have; hard drives will fit into 3.5", while physical media devices like DVD or BluRays require 5" bays (though adaptors are also available to fit 3.5" drives into 5" bays). With single hard drives now reaching 3TB, I find full tower cases to be largely redundant, but if you’re keen for a large RAID setup then a full tower might be for you.

Typical desktop tower cases can house 3 or 4 hard drives, enough for a small RAID setup, while HTPCs will only hold 1, or 2 at most.

CPU Cooler & Fans

One thing even geeks forget is the size of the CPU cooler, particularly if you’re thinking of overclocking and therefore need something oversized. Unfortunately, this aspect of case sizing has no standard; you will literally have to take out your tape measure and compare lengths. This is the "Killer Whale"....

buying a new pc case

If you are overclocking, you’re probably also looking to keep the general case temperature down too, since all that CPU heat has to go somewhere. Look for a case with a strong air flow and removal filters. Conversely, don’t choose a case with so many fans if you’re building a low power HTPC; silence is the key here.

Cost and Build Quality

When I was at university, I used my staff discount at Maplin to buy a beautiful Lian-Li case - and to this day, it still houses my main PC. No doubt it was pricey at around $200, but as components have been upgraded, and through multiple motherboard changes, it has stood by me solid as a rock. The Aluminium (and yes, I am spelling that right) makes it light as a feather to carry around; cheaper cases made of steel will give you a back injury when fully loaded. It has thumbscrews throughout, with removal drive caddys, and even a motherboard tray that slides out effortlessly - and no case has ever been as easy to work with.

This is why I’ve kept it for nearly 10 years now, and this is the difference that spending a little more on a good case will make to you.

buying a pc case

Don’t buy the cheapest one you can find because it’s "just a case", certainly if you ever plan on opening it up again to tinker with hardware - believe me when I say your time and frustration is worth more than that.

Do you have any other tips or advice on what to look out for when buying a PC case? Do you have a favourite case that has stayed with through numerous upgrades?

Image credit: Building a PC via Shutterstock