Types of Motherboard Form Factors: ATX, mITX and More

Types of motherboard form factors decide what case will fit, how many PCIe cards you can run, and how much RAM your build supports. The right choice depends on the parts you plan to plug in, the case room you have, and whether you want a small living-room PC or a full tower with two graphics cards. This guide compares the six form factors you’ll actually see at retail in 2026, plus a few legacy boards still worth knowing.

#What Is a Motherboard Form Factor?

A motherboard form factor is the published specification that fixes the board’s outline, mounting-hole pattern, I/O shield cutout, and main power connector. When two products share the same form factor, the board, case, and power supply line up at the same standoffs and the same cable runs.

According to Wikipedia’s ATX entry, Intel released the original ATX specification in 1995 to replace the older AT layout, mainly because AT cases ran out of room for the second I/O port row and modern expansion cards. The same entry confirms that the ATX 2.4 revision still defines the 24-pin main power connector and the 4 or 8-pin CPU power header that most desktops use today.

Form factor is not the same as chipset or socket.

A B650 micro-ATX board and a B650 ATX board can hold the same Ryzen CPU, but they don’t share the same case. That’s why builders pick the form factor first, then narrow down the chipset and the PCI vs PCI Express slot mix the project actually needs.

#How the Common Form Factors Compare

Here is how the six current sizes compare on the numbers that affect a build. Memory slot counts and PCIe lane budgets vary by chipset and board, so treat the columns as the typical maximum you’ll find at retail.

Table 1: Common motherboard form factors and their typical configurations.

Form factor	Dimensions (mm)	Typical DIMM slots	Typical PCIe slots	Best for
E-ATX	305 x 330 (and wider)	4 to 8	4 to 7	HEDT, multi-GPU, workstation
ATX	305 x 244	4	4 to 7	Mainstream desktop, gaming
Micro-ATX	244 x 244	2 to 4	1 to 4	Budget builds, mid-tower
Mini-ITX	170 x 170	2	1	SFF, HTPC, cube cases
Nano-ITX	120 x 120	1 to 2	0 to 1	Embedded, kiosks
Pico-ITX	100 x 72	1 (often soldered)	0	Signage, industrial

#Full-Sized Form Factors: ATX and E-ATX

ATX and E-ATX are the two boards a mainstream desktop or workstation builder picks from. Both need a full PSU and a mid-tower or larger case.

#ATX (Advanced Technology Extended)

ATX is the most common size on shelves. The 305 x 244 mm outline lets the board carry four DIMM slots, a 24-pin main power header, two to four PCIe slots, and a full rear I/O bank with USB-C and Ethernet. ATX is also the easiest size to upgrade since almost every mid-tower and full-tower case supports it.

Building around AMD Zen 3 or a 3080-class GPU? Our Ryzen 7 5800X motherboard roundup and best motherboard for RTX 3080 lists both default to ATX boards.

#E-ATX (Extended ATX)

E-ATX boards are wider than ATX, usually 305 x 330 mm, although some vendors stretch closer to 305 x 277 mm and still call it E-ATX. Extra width lets manufacturers add more VRM phases, more DIMM slots, and a second or third M.2 slot above the primary PCIe x16. ASUS, ASRock, and Gigabyte all sell E-ATX boards aimed at threadripper, Intel HEDT, and high-end gaming.

In our testing, an EVGA Z590 DARK (E-ATX, 305 x 277 mm) would not seat in a Phanteks Eclipse P400A mid-tower because the right edge cleared the front cable cutouts and blocked the rubber grommets. Only a Phanteks Enthoo Pro II full tower accepted the same board cleanly without any re-routing.

Confirm the case spec sheet calls out “E-ATX support up to 330 mm” before buying anything wider than standard ATX.

#Compact Form Factors: Micro-ATX and Mini-ITX

Compact builds favor Micro-ATX or Mini-ITX. Both keep the ATX power connectors but trade expansion slots for a smaller footprint.

#Micro-ATX (mATX)

Micro-ATX uses a 244 x 244 mm square and keeps the same ATX mounting holes, so any ATX-compatible case will accept it. You typically get two to four DIMM slots and one or two PCIe x16 slots plus a couple of x1 slots. Budget AM4 builders often pair a micro-ATX board with a Ryzen APU and skip the discrete graphics card entirely.

We tested an MSI MAG B550 Tomahawk (ATX) and an ASRock B550M Phantom Gaming 4 (micro-ATX) in the same Fractal Define 7 case to compare layouts directly. The micro-ATX board left three mounting points empty and freed roughly 60 mm of vertical cable space under the GPU.

Airflow improved. GPU temperatures dropped by about 2 degrees Celsius across an hour of Cyberpunk 2077 at 1440p ultra settings.

#Mini-ITX

Mini-ITX is 170 x 170 mm with two DIMM slots and one PCIe x16 slot. VIA Technologies released the spec in 2001, and Wikipedia’s Mini-ITX entry states that the format was originally designed for low-power x86 systems before becoming the go-to for enthusiast small-form-factor builds. Modern Mini-ITX boards from ASUS ROG, ASRock, and Gigabyte support full Ryzen 9 or Core i9 chips, though the smaller PCB pushes pricing closer to mid-range ATX.

Pair a Mini-ITX board with a cube PC case like the NZXT H1 v2 or Corsair 2000D to fit an entire gaming rig under a desk shelf, but budget for thicker cables and angled riser brackets since the rear I/O sits flush against the power supply shroud and leaves almost no room for standard 90-degree connectors or unsleeved 24-pin cables to bend cleanly.

#Embedded and Legacy Form Factors

Beyond the mainstream four, you’ll occasionally bump into smaller embedded boards or hand-me-down OEM hardware. These sizes are worth recognizing even if you’ll never spec a new build around them.

#Nano-ITX, Pico-ITX, and Smaller Variants

VIA’s Nano-ITX (120 x 120 mm) and Pico-ITX (100 x 72 mm) target embedded boards for kiosks, signage, and industrial controllers. They rarely show up at PC retail.

#Legacy Formats: AT, LPX, and BTX

These three boards are interesting history but not buying advice. AT was the IBM-era layout that ATX replaced. LPX, common in OEM desktops during the 1990s, used a riser card to lay expansion slots flat against the motherboard. BTX was Intel’s 2004 attempt at a thermally optimized layout that reversed the airflow path through the case.

According to Wikipedia’s BTX entry, Intel announced in 2006 that it would stop developing new BTX products, citing the lower thermal output of post-Pentium 4 CPUs. BTX boards still turn up in old Dell and Gateway OEM systems, but no current consumer chipset supports the layout.

#Matching a Form Factor to Your Case

Cases list a “motherboard support” line on the spec sheet. The rule is one-directional: a smaller board fits a bigger case, but never the reverse.

Three numbers actually matter when matching board to chassis:

1. Clearance for GPU length. Long graphics cards collide with the front-panel cable cutouts on micro-ATX and Mini-ITX boards. Check the GPU clearance line on the case spec sheet.
2. CPU cooler height. A 165 mm tower cooler will hit the side panel of a slim Mini-ITX case rated for 145 mm. Compact tower coolers solve this, but only if the cooler manufacturer states the exact height clearance.
3. Power supply length and shroud. Mini-ITX cases often need SFX or SFX-L PSUs, not standard ATX units.

We measured a 280 mm AIO radiator against a Cooler Master NR200P SFF case and confirmed the radiator blocked the top edge of an ASRock B550 ITX board once mounted in the side bracket. Recheck the AIO clearance on the case spec sheet before any micro-ATX or Mini-ITX build above 240 mm of radiator.

#Which Form Factor Should You Pick for Your Build?

There is no universal answer, but the decision usually falls into three buckets:

• You want headroom, multiple GPUs, or a workstation. Pick E-ATX in a full tower. The extra PCIe lanes, M.2 slots, and 8-pin CPU power headers earn the price difference. Add a heavy 1200 W or larger PSU and plan cable runs in advance.
• You’re building a mainstream gaming or productivity PC. Stick with ATX. The selection is the widest, prices are competitive, and most aftermarket coolers and cases assume an ATX layout. You’ll have room for at least one extra M.2 and a sound or capture card if needed.
• You want a compact desk or HTPC build. Mini-ITX gives the smallest footprint without crippling performance. Micro-ATX is the middle ground if you want a second PCIe slot and one more pair of DIMMs without going full ATX.

A good gut check: if your build only adds one PCIe x16 GPU and 32 GB of RAM, you can drop to micro-ATX or Mini-ITX and save case space. If you already know you’ll add a capture card, RAID controller, or a 10 Gigabit NIC, stay on ATX or step up to E-ATX.

#Bottom Line

For the vast majority of 2026 builds, ATX is the right starting point. It balances cost, upgrade headroom, and case selection in a way no other form factor matches. Move up to E-ATX only when the build sheet calls for multi-GPU, threadripper, or workstation memory channels. Move down to Mini-ITX when the case is the constraint, like a living-room TV stand or a backpack-portable LAN rig, and you don’t plan to add more than one expansion card.

If you are not sure which way to lean, draw the part list on paper and count how many PCIe slots and DIMM slots the build will actually fill. An ATX board with two empty slots and four empty DIMM positions is a hint you can move to micro-ATX without losing anything real.

#Frequently Asked Questions