Case sizes are the part of PC building with the vaguest names. ATX, Micro-ATX and Mini-ITX are real standards with real measurements, but mid tower, full tower and compact are marketing labels that mean whatever the case maker wants. The result is people buying a case that swallows their parts with room to spare, or one that leaves a graphics card a quarter inch too long. We assemble builds in every size at our Somerville shop. Here is what each name actually means, the clearance numbers that decide whether your parts fit, and the size we recommend for most people.
Case sizes follow motherboard sizes. These are the standard dimensions Intel lists in its motherboard buying guide, and every case spec sheet refers to them.
| Form factor | Board size | Expansion slots | Memory slots | Typical use |
|---|---|---|---|---|
| E-ATX | 12 x 13 in (305 x 330 mm) | Up to 7 | 4 to 8 | Workstation and flagship boards. Needs a case that lists E-ATX support; some "mid towers" do, most do not. |
| ATX | 12 x 9.6 in (305 x 244 mm) | Up to 7 | 4 | The default for gaming builds. Most M.2 slots, most ports, easiest to work on. |
| Micro-ATX | 9.6 x 9.6 in (244 x 244 mm) | Up to 4 | 4 on most boards | Same CPUs and memory as ATX in a shorter board. Usually cheaper. Fits ATX cases too. |
| Mini-ITX | 6.7 x 6.7 in (170 x 170 mm) | 1 | 2 | Small form factor builds. One graphics card, two memory sticks, usually two M.2 slots. Board prices run higher than Micro-ATX. |
Dimensions from Intel's gaming motherboard buying guide. Mounting holes are standardized, so a smaller board fits in a larger case (Micro-ATX in an ATX case, Mini-ITX in almost anything) but never the reverse.
Tom's Hardware's form factor guide makes the point plainly: "mid tower" and "full tower" describe a style, not a standard. Here is how the labels usually shake out in 2026.
| Case class | Typical height | Boards it takes | What you get | Trade-off |
|---|---|---|---|---|
| Full tower | 20 to 24 in (500 to 600 mm) | E-ATX, ATX and smaller | Room for 360 mm or 420 mm radiators top and front, a dozen drives, custom water cooling loops, and the longest graphics cards made. | Big, heavy, and more case than a gaming build uses. Often no cheaper per feature than a good mid tower. |
| Mid tower | 17 to 19 in (430 to 480 mm) | ATX and smaller (some list E-ATX) | Fits any mainstream graphics card, tower air coolers up to about 170 mm, and a 360 mm radiator in most models. The widest choice of cases at every price. | Almost none for a gaming PC. This is the default for a reason. |
| Micro-ATX / compact tower | 14 to 17 in (350 to 430 mm) | Micro-ATX and Mini-ITX | A few inches shorter and usually $20 to $40 cheaper than a mid tower, with the same CPU, memory and graphics card options. | Fewer drive bays and fan mounts; check graphics card length, since some compact cases stop around 330 mm. |
| Mini-ITX / small form factor | Varies widely; the best ones are 10 to 20 liters | Mini-ITX only | A desktop that fits in a backpack or on a shelf. Modern SFF cases still take full-length cards and 240 mm radiators. | Harder to build in, warmer, needs an SFX power supply, and every part must be checked for fit. The case and board cost more, not less. |
Because the labels are loose, the only numbers that matter are on the spec sheet: maximum graphics card length, maximum CPU cooler height, supported radiator sizes, and the motherboard sizes the case accepts. Two current cases from the same maker show how much "mid" and "full" can differ. Fractal Design's North, a mid tower, lists 355 mm of graphics card clearance, 145 mm of cooler height, and measures 447 x 215 x 469 mm. The North XL, the full tower version, lists 413 mm of card clearance and 185 mm of cooler height at 503 x 240 x 509 mm, and adds E-ATX support. Same family, two inches taller, and the clearance numbers are what changed.
We check these on every build before a single part is ordered. They are the reason the same "mid tower" can be right for one parts list and wrong for another.
The card's length is on its spec page, and the case's maximum is on its spec page. Compare them with room to spare. Then remember the power connector: Nvidia's RTX 5080 Founders Edition is 304 mm long and two slots thick, and Nvidia's own page asks for an extra 36 mm of clearance for the 16-pin cable. Third-party versions of the same GPU are often longer and thicker than the reference card, so check the exact model you are buying.
Large tower air coolers run 155 to 170 mm tall. A case rated for 145 mm, like the Fractal North above, rules out most of them, which pushes you to a shorter tower or a liquid cooler. Our air vs liquid cooling guide covers that decision; the case decides whether you get to make it.
A case can support a 360 mm radiator in the front and only a 240 mm in the top, or the reverse. Radiator support also depends on the thickness of the radiator plus its fans, and on memory height on the motherboard. If you plan on an all-in-one cooler, match its size to the exact mounting position you intend to use.
Standard ATX supplies are 140 to 180 mm long; compact cases publish a maximum, and a 1000 W unit is often at the long end. Mini-ITX cases usually require the smaller SFX form factor, which costs more for the same wattage. Size the supply first with our PSU sizing guide, then confirm it fits the case.
Representative picks cross-checked against Tom's Hardware's tested best PC cases list (updated August 2026) and PC Gamer's roundup. Models change; the sizing logic does not.
| Build | Size we recommend | Why |
|---|---|---|
| Most gaming builds, $1,000 to $2,500 | ATX mid tower with a mesh front | Fits any current graphics card and cooler, easiest to build and upgrade, best airflow per dollar. Tom's Hardware's current picks in this class include the Fractal North and Lian Li Lancool 217. |
| Budget build, under $1,000 | Micro-ATX tower or a budget ATX mid tower | Saves $20 to $40 on the case and $20 to $60 on the board with no performance cost. Tom's Hardware's budget pick, the Montech TG3, is the type of case we mean. |
| Desk with no floor space, or a living room PC | Mini-ITX small form factor | Worth the premium when size is the whole point. Expect tighter cooling, an SFX power supply, and a part list that has been checked for fit twice. |
| Workstation with E-ATX board, custom loop, or eight-plus drives | Full tower | The only builds that use the space. Tom's Hardware's full tower pick is the Cooler Master Cosmos Alpha. See our workstation build guide. |
| Quiet build | ATX mid tower with sound damping, or a solid-front case with good rear exhaust | Case choice is half of the noise result. We explain the rest in Quiet PC Builds. |
If you want specific models rather than sizes, our best PC case for custom gaming builds post covers the cases we reach for most. The sizing rules above are what we apply before any of those names come up.
⚡ Bought parts and not sure they fit the case? Bring the boxes in. We check clearance, swap the case if we have to, and build it right. If you are still choosing, tell us the parts and the desk it is going on and we will size the case for you.
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Cases are sized by the motherboards they hold. The standard board sizes are E-ATX (12 x 13 in), ATX (12 x 9.6 in), Micro-ATX (9.6 x 9.6 in) and Mini-ITX (6.7 x 6.7 in). Case classes built around them are full tower, mid tower, compact Micro-ATX towers and small form factor Mini-ITX cases. Mid tower and full tower are descriptive labels, not standards, so always read the case's own clearance numbers.
Roughly two to four inches of height and what that space allows. A full tower typically adds E-ATX support, longer graphics card clearance, taller cooler clearance, more radiator positions and more drive bays. For example, Fractal's North mid tower lists 355 mm card and 145 mm cooler clearance; its North XL full tower lists 413 mm and 185 mm. Most gaming builds do not use the extra room.
Micro-ATX if you want a smaller PC without giving anything up: it takes the same CPUs, four memory slots and up to four expansion slots, and it is usually the cheapest board and case combination. Mini-ITX if small is the goal: one expansion slot, two memory slots, a higher board price, an SFX power supply and careful part selection.
Yes. The mounting holes are standardized, so a Micro-ATX or Mini-ITX board fits in any ATX case. The reverse is not true: an ATX board will not fit a Micro-ATX or Mini-ITX case.
Compare the card's listed length to the case's maximum card length, allowing for any front radiator or fans, and check the card's thickness in slots against the case. Add clearance for the power cable: Nvidia asks for 36 mm beyond the RTX 5080 Founders Edition's 304 mm length for the 16-pin connector. Partner cards are often larger than the reference design.
Not by itself. Airflow design matters more than volume: a mid tower with a mesh front and a sensible intake and exhaust layout usually runs cooler than a larger case with a solid front panel. Bigger cases do make room for larger radiators and more fans, which helps only if you install them.
Bring your parts list or your boxes. We will check every clearance, pick the right size for your desk, and assemble it so the first boot is the only boot.
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