Motherboards come in a few standard sizes called form factors. The size decides which cases the board fits in, how many RAM sticks and expansion cards it takes, and how small your finished PC can be. Here's how to choose, and how to make sure everything fits together.
The main sizes
| Form factor | Size | RAM slots | Good for |
|---|---|---|---|
| ATX | 305 × 244 mm | 4 | Most builds: room for extra M.2 slots, PCIe cards, fan headers |
| Micro-ATX (mATX) | 244 × 244 mm | 2–4 | Budget and mid-range builds, smaller towers |
| Mini-ITX | 170 × 170 mm | 2 | Small, compact PCs |
| E-ATX | 305 × up to ~330 mm | 4–8 | High-end workstations and enthusiast builds |
The performance is the same across sizes. A Ryzen 7 runs just as fast on a Mini-ITX board as on an ATX board, as long as the board's power delivery is good enough for the CPU. What changes is space for extra parts, cooling and connectivity.
How to read the size from a board's name
Store listings don't always state the size, but the model name usually does:
- "M" after the chipset means Micro-ATX: B650M, B760M-A, H610M-S.
- "I" after the chipset means Mini-ITX: B650I, Z890I Nova.
- No letter usually means full ATX: B650 Tomahawk, X870 Gaming X.
Our builder reads this automatically. When a listing doesn't say the size and we infer it from the name, the specs show "(likely)" so you know to double-check.
Which size should you choose?
ATX: the safe default
ATX boards have the most M.2 slots, the most fan and USB headers, and room for a second graphics slot or capture card. Choose ATX if you want flexibility and have space for a mid-tower case.
Micro-ATX: best value
Micro-ATX boards are often the cheapest way onto a platform and fit in smaller, cheaper cases. Most gaming builds only use one graphics card and two RAM sticks anyway. Check the number of M.2 slots if you plan to add storage.
Mini-ITX: small and stylish, with trade-offs
Mini-ITX makes a compact PC that's easy to move, but it limits you to two RAM sticks, usually two M.2 slots and one PCIe slot. Small cases also mean tighter limits on GPU length, cooler height and PSU size, and they can run warmer. Plan carefully, and maybe avoid ITX for your first build.
Four checks to make sure your case fits
- Motherboard support. The case must list your board size. Bigger cases fit smaller boards: an ATX mid-tower takes ATX, Micro-ATX and Mini-ITX boards. A Micro-ATX case takes Micro-ATX and Mini-ITX only.
- Graphics card length. Compare the card's length (often 250–340 mm for modern cards) with the case's "max GPU length". Front radiators reduce that space.
- CPU cooler height. Tower air coolers are often 150–165 mm tall. Check the case's "max CPU cooler height". If you're using liquid cooling, check which radiator sizes it supports (240/280/360 mm) and where.
- Power supply size. Most cases take standard ATX PSUs. Many small ITX cases need a smaller SFX PSU.
The builder checks board size against the case automatically. GPU length and cooler height aren't in most store listings, so check those on the product pages.
Airflow matters more than looks
A case with a mesh front panel and at least two intake fans keeps everything cooler and quieter. That makes a real difference in Lebanese summers, when room temperatures are high, especially during power cuts when the AC is off. Glass-front cases look great but often run hotter unless they have side vents. Our cooling guide covers fan layouts.
Frequently asked questions
Can I put a Micro-ATX board in an ATX case?
Yes. ATX cases have the mounting holes for Micro-ATX and Mini-ITX boards too. The reverse doesn't work: an ATX board won't fit a Micro-ATX case.
Is Micro-ATX worse than ATX for gaming?
No. Gaming performance depends on the CPU, GPU and RAM, not the board size. Micro-ATX boards just have fewer extra slots and connectors.
What does "E-ATX support" on a case mean?
The case is large enough for extended ATX boards. It also fits ATX, Micro-ATX and Mini-ITX boards.
Do cases come with fans?
Many do, often 1–4 fans. Listings like "with 4 ARGB fans" include them. Budget cases sometimes ship with one rear fan only, so plan to add intake fans at the front.