Contrary to Yoda's wisdom, size does matter with PC cases—a lot. Cases come in three major types: ATX, MicroATX, and Mini-ITX. These correspond to the three main form factors of motherboard; case categories follow these motherboard standards. (For a kick-start to understanding desktop mainboards, see our guide to the best motherboards, and our primer Buying a Motherboard: 20 Terms You Need to Know.)

The most common case type is the ATX chassis, which accommodates ATX motherboards (far left in the picture below). These boards typically measure 12 by 9.6 inches, and an ATX case has mounting holes in a standardized layout to match boards of that size.

The lion's share of ATX cases are classed as "mid-towers" or "full towers," which are inexact terms that refer to the case's exterior dimensions. Full towers, which are larger, feature extra bays inside for storage drives and more room for larger cooling hardware. Some full towers also work with the less common 12-by-13-inch Extended ATX (EATX) motherboard standard. That board size is mainly used for so-called high-end desktop (HEDT) builds, with the boards supporting Intel Xeon or AMD Ryzen Threadripper processors. Most motherboards for mainstream AMD Ryzen or Intel Core processors are ATX or smaller.

Mini-ITX motherboards (on the far right in the board comparison photo above), at 6.7 inches square, are on the opposite side of the size spectrum from ATX and EATX. Meanwhile, MicroATX boards (middle in the photo) measure 9.6 inches square. MicroATX is a compromise size. Most ATX cases are compatible with these smaller motherboards, as well, via alternate mounting points.

Likewise, most MicroATX cases accept smaller Mini-ITX boards, in addition to (of course!) MicroATX ones. But the whole point of buying and using a smaller-than-ATX motherboard is to install it in a smaller-than-ATX case. So, as a general rule, the case you buy really should match the motherboard standard you're using.

Note: One trend spreading these days among motherboards (and thus PC cases) is the "reverse connector" motherboard. Mostly from Asus (dubbed Back to the Future, aka BTF) and MSI (Project Zero), these aesthetics-minded motherboards have their cable connectors on the rear side, allowing you to hide cables behind the board and run them out of sight. The idea is to allow for a clean-looking build inside your case, which presumably has one more transparent sides to show off the "Look Ma, no cables!" motif. These motherboards require, however, a PC case that has cutaways in the motherboard tray to accommodate their underside connectors. When looking at motherboard compatibility for a given case, you may see mention of support for one or both of these board designs. Opt for the right kind if you're getting one of these special motherboards.

The best desktop builds start with the right case. Once you know the motherboard standard you'll be using (such as ATX or Mini-ITX), you'll know the minimum size case required for your build. The case must have enough bays for your storage drives, enough room for your graphics card, and any necessary headroom for cooling devices such as liquid-cooling radiators. 

Beyond the functional aspect, case buying comes down to aesthetics and preferences. Don't be afraid to spend extra for an attractive case made of quality materials like aluminum or tempered glass. The case is, after all, a reflection of your build and what you put into it, and it may survive multiple PC iterations, outliving what's inside.

When you consider that you can reuse your case for future builds, the money you spend on the right model can go further than you think. So don't repress your PC's personality, or your own: Check out a host of our favorites here as a launching point for your case search.

PC cases that provide a view of the interior practically beg for internal lighting to show off your components. Nowadays, almost every PC part, from graphics cards and CPU coolers to memory modules and even SSDs, can be found with LED decoration. But the brunt of illumination in most aftermarket cases that emphasize RGB is done by discrete light sources in the case itself, usually LED-equipped case fans and light strips. 

Many cases will include pre-installed LED fans, though don't assume one LED fan is as decent as another—their brightness and color intensity can vary greatly. For those extra sensitive to how the lighting will look, it's often better to buy a case without LED fans (or any fans at all) and then install higher-quality fans of your choosing. (See the airflow section below for more on installing your own fans.)

Basic case lighting pre-installed in a cheaper case may just be a single color of LED, or the lights may cycle through a preset menu of colors and effects via a button or control on the front panel. The more advanced form of LED lighting is RGB, which supports the 16.7 million colors of the RGB color spectrum. Controlling those colors can be a complex business, or at least as complex as you want it to be.

Most RGB fans, light strips, and other components nowadays will connect to a standard RGB or an Addressable RGB (ARGB) header connector, either on the motherboard or on a controller box that connects to the motherboard. An ordinary RGB header connection will simply cause the lights to illuminate, but the ARGB type gives you far more granular control. It opens a lot of possibilities when it comes to strobing, pulsing, and color changing, as well as coordinating effects across supported LED-equipped components.

The RGB gear in the case may be affiliated with a given case maker's light control solution, like Corsair's or Razer's, or it may work with the RGB-control software provided by a motherboard maker, such as Asus (Aura Sync), MSI (Mystic Light), Asrock (Polychrome), or Gigabyte (RGB Fusion). You'll want to look for what RGB standards the case lighting adheres to, to see if it syncs, no pun intended, with other hardware you own, especially a motherboard's control scheme.