ATX, Micro ATX and Mini ITX are motherboard form factors. They mainly change the physical size of the board, how many expansion slots and connectors can fit on it, and what size PC case you need.
For most builders, ATX is the easiest all-round choice, Micro ATX is the best value compact option, and Mini ITX is for genuinely small builds where space matters more than expandability.
ATX vs Micro ATX vs Mini ITX at a glance
| Form factor | Typical size | Best for | Main trade-off |
|---|---|---|---|
| ATX | 305 × 244 mm | Mainstream gaming, workstations, easy upgrades | Needs a larger case |
| Micro ATX | 244 × 244 mm | Value builds and compact towers | Fewer expansion slots |
| Mini ITX | 170 × 170 mm | Small-form-factor PCs | Least expansion room; tighter cooling/layout |
Intel’s current motherboard buying guide lists the same standard dimensions and notes that larger boards generally offer more DIMM, PCIe and M.2 slots.
ATX: the easiest choice for most full-size PCs
ATX is the standard 12 × 9.6-inch desktop motherboard size. A typical consumer ATX board can provide up to seven expansion-slot positions and usually has four DIMM slots.
The practical advantage is room. ATX boards have more space for PCIe slots, M.2 storage, fan headers and other connectors, and the cases that fit them normally leave more working room around the graphics card, CPU cooler and cables.
Choose ATX if you want the least stressful build process or expect to add capture cards, extra storage controllers, networking cards or other expansion hardware later.
Micro ATX: often the best value
Micro ATX is 9.6 × 9.6 inches, so it is shorter than ATX but still large enough for a conventional desktop build. Many Micro ATX boards retain four memory slots and enough PCIe expansion for a graphics card plus another device.
The biggest advantage is value. You can often build a smaller PC without paying the small-form-factor premium associated with Mini ITX.
Micro ATX also fits in many ATX cases, although you should always check the case’s motherboard support before buying.
Mini ITX: smallest, but not automatically better
Mini ITX measures 6.7 × 6.7 inches (170 × 170 mm). It is designed for compact systems and normally has a single full-length PCIe slot and two DIMM slots.
That does not mean Mini ITX is slower by definition. A small motherboard can use the same CPU and high-end GPU as a larger board if the chipset, power delivery and cooling design support them.
The trade-offs appear elsewhere: fewer expansion slots, fewer memory slots, tighter M.2 placement, more difficult cable routing and more demanding cooling. Mini ITX motherboards can also cost more because manufacturers have to fit a lot of circuitry into a very small area.
Does motherboard size affect gaming performance?
Not directly. Form factor does not determine frame rate. A Mini ITX motherboard and an ATX motherboard using the same compatible CPU, GPU, memory settings and similar power limits can deliver essentially the same gaming performance.
What changes is how easy it is to support the rest of the system. A larger board may offer more PCIe slots, more M.2 sockets, stronger cooling around the VRM, additional fan headers or more convenient component spacing.
Case compatibility matters more than the label on the box
Do not assume every “mid tower” supports every board. Check the case specification for explicit ATX, Micro ATX or Mini ITX support.
As a general rule, a case designed for ATX often accepts Micro ATX and Mini ITX as well, but the reverse is not true. A compact Micro ATX case will not normally fit a full ATX motherboard.
Expansion slots and GPU clearance are different problems
Motherboard size affects how many expansion slots are available, but your graphics card also needs physical clearance in the case. A three- or four-slot GPU can cover neighbouring motherboard slots regardless of form factor.
If you are planning a high-end GPU, check the case’s maximum GPU length and thickness as well as motherboard support.
RAM capacity: don’t assume Micro ATX means only two slots
A common myth is that smaller always means fewer RAM slots. Many Micro ATX boards have four DIMM slots, just like ATX. Mini ITX boards typically have two.
Always check the exact board, because form factor sets physical constraints rather than a universal feature list.
Cooling and CPU cooler clearance
The motherboard form factor itself does not set the maximum CPU cooler height. The case does. Small-form-factor cases often require low-profile air coolers or carefully chosen liquid-cooling layouts.
For an example of why cooler dimensions matter, see our CPU cooler guide.
Power supply compatibility
ATX, Micro ATX and Mini ITX motherboards can all use standard desktop power connectors, but small cases may require a physically smaller SFX or SFX-L power supply instead of a full ATX PSU.
If you are upgrading an existing PC and are unsure what is already installed, see how to check what power supply you have.
Which motherboard form factor should you choose?
- Choose ATX if you want maximum flexibility, easier building and plenty of expansion.
- Choose Micro ATX if you want a smaller, often cheaper system without giving up normal gaming performance.
- Choose Mini ITX if the small size of the finished PC is a major goal and you accept higher cost and tighter component planning.
For most gaming PCs, Micro ATX and ATX are the sensible starting points. Mini ITX is excellent when you specifically want a small-form-factor build, but it should be a deliberate choice rather than an assumption that smaller means newer or faster.
