What size PC case do I need?

NZXT H2 Flow small form factor case in white on a desk next to a monitor, speaker, keyboard and mouse, front three-quarter view with a liquid cooler visible through the glass — The H2 Flow, a Mini-ITX case, on a desk next to a monitor and speaker.

The PC case size you need depends on your motherboard form factor first, then on your graphics card length and cooling plan. An ATX motherboard needs an ATX-compatible case, usually a mid-tower. Micro-ATX and Mini-ITX boards fit smaller cases. Before you buy, always confirm GPU length, CPU cooler height and radiator support.

Case names like "mid-tower" and "full tower" aren't standardized, so the listed clearances matter more than the label. Here's how to match a case to your parts.

What motherboard sizes are there?

The four common desktop motherboard sizes are Mini-ITX, Micro-ATX, ATX and E-ATX. The board you choose sets the minimum case size, because every case lists the board sizes it can mount.

Form factor	Board size	Max expansion slots	Typical case
Mini-ITX	170 x 170 mm (6.7 x 6.7 in)	1	Small form factor
Micro-ATX	Up to 244 x 244 mm (9.6 x 9.6 in)	4	Micro-ATX or compact mid-tower
ATX	305 x 244 mm (12 x 9.6 in)	7	Mid-tower
E-ATX	Wider than ATX; varies by board	Typically 7	Large mid-tower or full tower

Source: Intel ATX Specification, Version 2.2 (ATX). Micro-ATX and Mini-ITX dimensions are defined in the Intel microATX and VIA Mini-ITX specifications.

Smaller boards fit in larger cases: an ATX case almost always accepts Micro-ATX and Mini-ITX. The reverse isn't true. E-ATX has no single fixed width, so check the case's listed E-ATX limit against your board's actual dimensions.

What's the difference between a mid-tower and a full tower?

A mid-tower typically fits ATX boards and most gaming hardware. A full tower is larger and usually adds room for E-ATX boards, more radiators and more drives. Because neither term has an official definition, compare listed volume and clearances instead of relying on the label.

Volume in liters is a useful single number for overall size. Clearance specs tell you whether your parts will actually fit.

How do I check if my graphics card will fit?

Compare your GPU's length, from the card maker's spec sheet, with the case's listed GPU clearance, and use the clearance that matches your planned fan or radiator setup. Many cases list several GPU lengths because front fans and radiators take up space.

For example, the H3 Flow lists up to 377 mm without front fans, up to 352 mm with front fans, and up to 317 mm with a front radiator and fans. The same case can fit a long card or a front radiator, but maybe not both. Also check:

Thickness and width, especially in small form factor cases with vertical GPU mounts.
Expansion slots, since thick cards can cover three or more slots.
Power connector clearance: leave room for the power cable to exit the card without a sharp bend against the side panel.

How do I check radiator and CPU cooler fit?

For a liquid cooler, check radiator size support at the exact location you plan to mount it, and the case's "radiator + fan thickness" limit. For an air cooler, compare the cooler's height with the case's CPU cooler height clearance.

NZXT H9 Flow in white, straight-on left side view of a build with a liquid cooler radiator mounted at the top and three fans on the front-right side — An H9 Flow build with a top-mounted radiator. Check radiator length and the clearance above the motherboard before you buy.

Radiator size by location. A case might take a 420 mm radiator in the front but only 360 mm on top.
Radiator + fan thickness. A radiator plus its fans can be thicker than the space available above the motherboard, especially with tall memory.
CPU cooler height. Tower air coolers vary widely in height, and small cases often have tight limits.
PSU length. Long power supplies can collide with bottom fans or drive cages.

Which case size is right for my build?

Choose the smallest case that fits your motherboard, GPU and cooling plan with some breathing room. Smaller cases save desk space but give you less room to work and fewer cooling options. Larger cases are easier to build in and take more radiators and fans.

Mini-ITX: best when desk space matters most. Expect SFX power supplies, low-profile coolers or a single front radiator, and careful cable planning.
Micro-ATX: a balanced middle ground with room for a full-size GPU and a 240 mm or 280 mm radiator in many cases.
ATX mid-tower: the default for most gaming builds. Wide hardware support, easy to build in.
Large mid-tower or full tower: for E-ATX boards, multiple large radiators, very long GPUs or lots of fans.

What do NZXT cases look like at each size?

Here are three NZXT cases across the size range, using their listed specs:

NZXT H2 Flow in white, front-left three-quarter view of a Mini-ITX build with a liquid cooler visible through the side glass — Mini-ITX: the H2 Flow.

NZXT H3 Flow in white, front-left three-quarter view of a Micro-ATX build with a top-mounted liquid cooler, graphics card and a perforated bottom shroud — Micro-ATX: the H3 Flow.

NZXT H9 Flow in white, front-left three-quarter view of a full build with a top-mounted liquid cooler, graphics card and front-right fans — Large mid-tower: the H9 Flow.

H2 Flow is a 20.7 L small form factor case for Mini-ITX boards. It takes SFX and SFX-L power supplies, GPUs up to 331 mm, and a front radiator up to 280 mm. View product
H3 Flow is a 35.0 L Micro-ATX case with a front radiator up to 280 mm and CPU coolers up to 170 mm tall. View product
H9 Flow is a 76.7 L mid-tower that supports E-ATX boards up to 277 mm wide, radiators up to 420 mm on the top and front, and GPUs up to 459 mm (with fans under 56 mm thick at the front). View product

Compare every size in PC cases.

Quick checklist

Confirm your motherboard form factor and, for E-ATX, its exact width.
Check the case's GPU length for your planned front fan or radiator setup.
Check GPU thickness and expansion slot count, especially for small form factor cases.
Match radiator size to a specific mount location, then check radiator + fan thickness.
For air cooling, compare cooler height with the case's CPU cooler clearance.
Confirm PSU form factor (ATX or SFX) and maximum PSU length.
Measure your desk, then compare it with the case's listed dimensions.

FAQ

Can I put a Micro-ATX motherboard in an ATX case?

Yes. ATX cases include mounting points for Micro-ATX and usually Mini-ITX boards. You'll have extra room and possibly some unused expansion slot covers.

Is a mid-tower big enough for a high-end GPU?

Often, yes. Many mid-towers list GPU clearance above 400 mm. Check the clearance that applies with your front fans or radiator installed, because that number can be lower than the headline figure.

What's the difference between ATX and E-ATX cases?

E-ATX boards are wider than ATX. Cases that support them list a maximum E-ATX width, and boards beyond that width won't fit or may block cable routing holes.

Do small form factor cases need special parts?

Usually. Many Mini-ITX cases require SFX or SFX-L power supplies and limit CPU cooler height and GPU thickness. Check every clearance spec before you buy parts.

Does a bigger case run cooler?

Not by size alone. A bigger case usually has more fan and radiator mounts, which helps, but cooling depends on how many fans you run and how air moves through the case.