ATX vs Mini-ITX Motherboards
These are the two ends of the desktop range. ATX is the full-size 305 × 244 mm standard with up to seven expansion slots and, nearly always, four memory slots. Mini-ITX is a 170 mm square with one expansion slot and two memory slots. The processor and graphics card decide performance, not the board size, so this is a choice about how small the finished PC needs to be and what you will give up to get there.
The verdict
Build ATX unless the size is the point. Mini-ITX costs more per feature, halves your memory slots and leaves one expansion slot for the graphics card, and it makes cooling harder. Those are all reasonable trade-offs for a genuinely small PC, and poor ones for a normal tower.
The physical difference
These are fixed standards, the same for every board of that size.
Cases, cooling and what fits
Most of what people worry about here is decided by the case, not the board.
Which case takes which board
A case is built around one board size and accepts that size plus anything smaller, never anything larger. So a case rated for the larger of these two will happily take the smaller one, using a different set of standoffs, while the reverse does not physically fit. Picking the smaller board does not commit you to the smaller case.
Cooler height and graphics card length
Both limits are published by the case, not the board, and they are the two numbers most likely to catch you out in a small build. Check the maximum CPU cooler height and maximum graphics card length on the case you have in mind before you order either part.
What you give up, in numbers
How the two sizes actually differ once you look at every board on sale, rather than at what the standard permits. Measured across 217 ATX and 22 Mini-ITX boards at the retailers we track (201 and 18 in stock today), and updated daily.
The picks on each side
The cheapest board on each side, and the cheapest one that clears a floor worth clearing: enough power headroom for the socket’s top processor, and Wi-Fi 6E or better. Recalculated daily from live prices.
ATX
Best all-round
$118.99 · cheapest with the power headroom and Wi-Fi worth having
Mini-ITX
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Common questions
Is Mini-ITX worth it over ATX?
Only if you want a small PC. Mini-ITX boards usually cost more than a comparable ATX board, take half the memory, and leave a single expansion slot. What you get back is a machine that fits where an ATX tower will not.
Can a Mini-ITX board fit in an ATX case?
Yes. ATX cases carry the Mini-ITX mounting points, so the smaller board fits with a lot of room to spare. Most people pairing the two are doing it for a quiet build with generous airflow.
Do Mini-ITX motherboards limit performance?
Not the processor or graphics card themselves, which perform the same in either board. The practical limits are memory capacity from having two slots instead of four, one expansion slot, and less room for a large CPU cooler.
Keep going
Browse every ATX board or Mini-ITX board with filters, put two specific boards head to head, or read up on choosing a case to fit the board you pick.