ATX vs Micro-ATX Motherboards: What's the Difference?
The main difference between ATX and Micro-ATX motherboards is physical size. ATX measures 305mm × 244mm; Micro-ATX comes in at 244mm × 244mm. That size difference affects how many expansion slots you get, which cases will fit the board, and — to a lesser extent — your upgrade options down the line. For most gaming builds, both form factors are entirely capable. The choice usually comes down to what you actually need inside the machine.
Size and What It Actually Changes
ATX boards are larger and typically come with four RAM slots, more PCIe slots, and better spacing between components. Micro-ATX boards are smaller, usually still offer four RAM slots on mid-range and upper-end models (though some budget versions drop to two), and fit into a wider range of cases — including more compact mid-towers and smaller chassis that won't accommodate a full ATX board.
What a lot of people don't realise is that the size difference rarely affects core performance. The CPU socket, memory controller, and chipset are the same between ATX and Micro-ATX versions of the same chipset family. An AMD B650 ATX and a B650M Micro-ATX will run the same Ryzen processor at the same speeds. The silicon is identical. You're not getting a faster system by choosing a bigger board.
Expansion Slots: Where ATX Has a Genuine Edge
ATX boards typically have more PCIe slots. You might get two, three, or four x16/x1 slots versus one or two on a Micro-ATX. If you're only ever running a single GPU — which describes the vast majority of gaming setups — this makes zero practical difference. But if you're planning to add a dedicated sound card, a capture card, a second NVMe controller, or an additional networking card, those extra slots on an ATX board give you somewhere to put them without juggling priorities.
Most home gaming builds never fill more than one PCIe slot. I've built and repaired enough systems to say that confidently. The expansion arguments for ATX sound compelling on paper, but in practice, a Micro-ATX board rarely leaves anyone short.
Which Cases Fit Which Boards
This is where the decision gets more practical. Full ATX boards only fit in full-size mid-tower cases and larger. Micro-ATX boards fit in both mid-towers and Micro-ATX specific cases, which tend to be more compact. If you already own a case or have a specific chassis in mind, check its compatibility list before deciding on a form factor. A full-size mid-tower will accept both, so if you're building into something like a Fractal Design or be quiet! mid-tower, either option works.
One thing worth mentioning: smaller Micro-ATX cases can create tighter airflow situations depending on the layout. That's more a case problem than a motherboard problem, but it's worth considering if you're pairing a smaller chassis with a warmer GPU. If thermals are a concern for your build, have a read of our guide on how much PSU wattage you need for a gaming PC — wattage and heat are more connected than people think.
Price Differences: Real But Often Overstated
Micro-ATX boards are generally cheaper than their ATX equivalents — sometimes by £20–50 on comparable chipsets. Budget boards in the Micro-ATX segment do exist at lower price points, but so do quality mid-range and enthusiast-level Micro-ATX options. The cheap end of both markets tends to cut corners in similar ways: reduced VRM quality, fewer USB ports, basic audio implementation. Spending a bit more on either form factor usually gets you meaningfully better build quality.
Don't assume a Micro-ATX board is automatically the budget choice. A mid-range B650M can outperform a cheap ATX board in almost every measurable way.
The VRM Argument: Important but Nuanced
ATX boards often have better VRM implementations because the larger PCB gives manufacturers more room to work with. If you're buying a high-end CPU — say a Ryzen 9 or an Intel Core Ultra 9 — and planning to push it hard, the VRM quality on the motherboard genuinely matters for sustained performance. On those platforms, ATX boards from reputable manufacturers tend to offer better long-term stability under load.
That said, if you're running a mid-range CPU like a Ryzen 5 or Core i5, a decent Micro-ATX board's VRM will handle it without breaking a sweat. This argument only really applies at the top end.
Common Mistakes I See
One mistake that comes up regularly is people buying an ATX board simply because it looks more capable, then never using any of the extra slots or features. They end up paying more for things they don't need, which would have been better spent on the GPU or storage. The motherboard is not where gaming performance comes from.
The opposite mistake also happens: someone buys a dirt-cheap Micro-ATX board to save money, then pairs it with a high-end CPU and wonders why temperatures spike under sustained loads. VRM quality matters when the board is being asked to do serious work.
If you're unsure where to allocate budget in a new build, our best gaming PC build under £1000 article lays out how to balance spending across components sensibly.
ATX vs Micro-ATX: A Practical Summary
Choose ATX if:
✓ You're building into a full-size mid-tower and want flexibility for future expansion
✓ You're running a high-end CPU that benefits from stronger VRM headroom
✓ You plan to add multiple PCIe devices like capture cards or additional controllers
✓ You want more USB and fan header options from a single board
Choose Micro-ATX if:
✓ You want a compact or smaller mid-tower build without compromising on component quality
✓ You're running a mid-range CPU and don't need maximum expansion capacity
✓ Budget is tight and the savings go toward GPU or storage instead
✓ You only need one PCIe slot, which covers the overwhelming majority of gaming setups
What We'd Choose
For a typical gaming build with a Ryzen 5 or Core i5 equivalent, a solid Micro-ATX board on a B650 or B760 chipset makes complete sense. The money saved versus a comparable ATX board can go somewhere it actually improves the gaming experience. For anyone running a top-end CPU and pushing it regularly — or building a workstation that'll host several PCIe cards — ATX gives you the breathing room.
If you want to spec out a build with the right board for your budget, our build configurator at Rig & Revive lets you put a custom system together without overspeccing components you don't need.
Frequently Asked Questions
Is Micro-ATX good for gaming?
Yes, absolutely. Micro-ATX boards support the same CPUs, run the same speeds, and handle single-GPU gaming builds without any disadvantage over ATX. The size difference doesn't affect gaming performance.
Will an ATX board fit in a Micro-ATX case?
No. ATX boards are larger and won't fit into cases designed for Micro-ATX. However, a Micro-ATX board will fit into a standard full-size mid-tower case designed for ATX, so you have flexibility there.
Do ATX motherboards perform better than Micro-ATX?
Not inherently. Same chipset, same CPU support, same memory support. Higher-end ATX boards may have better VRM implementations, but that's a budget and tier comparison, not a form factor advantage.
Does Micro-ATX limit RAM capacity?
Not usually. Most Micro-ATX boards in the mid-range and above have four RAM slots, supporting the same DDR5 or DDR4 capacities as equivalent ATX boards. Some budget Micro-ATX boards drop to two slots, which is worth checking before purchasing.
Are Micro-ATX cases worth using for gaming?
They can be, though airflow management matters more in tighter enclosures. A quality Micro-ATX case from a reputable brand like Fractal Design or Corsair will handle a gaming build just fine. Cheap small cases with poor ventilation are where problems start.
Can I upgrade from Micro-ATX to ATX later?
Not without buying a new board and likely a new case. If you think you'll want significant expansion in the future, ATX is the safer long-term choice. If you're unlikely to add multiple PCIe devices, there's little reason to plan for it.
Is there a performance difference between B650 ATX and B650M Micro-ATX?
No. The chipset is the same. The "M" in B650M indicates Micro-ATX form factor, not a reduced-capability chipset. You're getting the same features in a smaller package.
The choice between ATX and Micro-ATX is less dramatic than people make it. Know what you're building, know what your case supports, and spend the rest of your budget where it actually moves the needle.