ATX vs microATX vs Mini-ITX: choose a PC case and motherboard
Start with the available space and expansion devices, then choose a case and motherboard together. Even a single thick graphics card can obstruct other slots. For a compact build, verify that the GPU, CPU cooler and power supply fit at the same time.
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Who this guide is for and what to prepare
- First-time builders choosing a case and motherboard
- People planning a smaller PC or adding expansion cards
What you need
- Measure the available width, height and depth, allowing room for cables and ventilation
- List the exact GPU, cooler, PSU, expansion-card and storage candidates
Board sizes and what the label does not tell you
ATX, microATX and Mini-ITX describe motherboard form factors. The table uses three B850 products as concrete examples; it does not assign their connector counts or performance to every board in the category.
More memory slots do not guarantee the same memory speed with all slots populated. Check support for the intended CPU and memory configuration.
Scroll horizontally to see the full table →
| Form factor | Example board | Board size | DIMM slots |
|---|---|---|---|
| ATX | ASUS PRIME B850-PLUS WIFI | 305 × 244 mm | 4 |
| microATX | ASUS PRIME B850M-A WIFI | 244 × 244 mm | 4 |
| Mini-ITX | ASUS ROG STRIX B850-I GAMING WIFI | 170 × 170 mm | 2 |
Choose the expansion capacity you need
An ATX label does not establish gaming performance. List the cards and SSDs beyond the GPU, then check usable slot positions, electrical lanes and shared connections.
On the PRIME B850-PLUS WIFI, for example, using certain PCIe slots disables shared SATA ports. Read the notes on simultaneous use instead of only counting connectors.
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| Use case | Starting point | Before buying |
|---|---|---|
| GPU plus capture or network cards | Compare ATX boards and their slot layout | Slots covered by the GPU and shared lanes |
| One GPU and the required SSDs | Include microATX candidates | M.2 slots, USB and fan headers |
| Fit a desk or confined space | Compare Mini-ITX with a matching case | PSU format and combined cooling clearance |
Read case support and mounting information
Mid-tower and mini-tower are case categories, but the name alone does not confirm that a particular board fits. Check the supported form factors, actual dimensions and restrictions around cable covers.
A front USB-C port also needs a compatible motherboard header. Match the case cable and board connector in their manuals; if an adapter is needed, check its capabilities and add its cost.
- Read the case specifications for supported board formats and dimensions.
- Match mounting holes and standoff positions to the case manual. Do not leave unnecessary standoffs beneath the board.
- List the connections for front USB, audio, switches and fans.
- Measure the space remaining for vents and cables after placing the case.
Compact cases can trade cooler space for GPU space
The Fractal Design Terra illustrates a shared-clearance constraint: moving its central plate changes the CPU and GPU chambers. For GPUs up to 131 mm tall, the official table allows a 77 mm CPU cooler with a 43 mm-thick GPU at position 1, or a 48 mm cooler with a 72 mm-thick GPU at position 7. Those separate maximum values cannot be combined.
GPU height changes the permitted thickness, while radiator installation introduces another GPU-length limit. Compare dimensions under the same configuration in the support table rather than ordering from the maximum GPU length alone.
- Find the exact GPU length, height and thickness.
- Check cooler height, fan placement, PSU format and PSU length.
- Choose a layout that satisfies all dimensions together, including power-cable routing.
Compare the complete cost of each layout
A smaller case is not automatically cheaper, and ATX is not automatically more expensive. Add any required replacement PSU or cooler to the case and motherboard cost. This article does not present a retail-price survey or a physically validated build.
Scroll horizontally to see the full table →
| Cost item | What to check |
|---|---|
| Case and motherboard | Required ports, expansion and supported dimensions |
| PSU and cooler | Whether existing parts meet format and mounting requirements |
| Fans, cables and riser | Included versus extra parts, supported interfaces and maintenance access |
| Shipping, assembly or inspection | Final charge, returns and warranty terms |
- Make two layouts with the same CPU, GPU and RAM capacity; price the parts that must change.
- Record unresolved dimensions and compatibility conditions for each layout.
- Resolve those items through manufacturer documentation or the retailer before ordering.
Limitations and requirements
- Physical fit does not establish CPU BIOS or memory compatibility.
- Named products illustrate dimensions and restrictions; they are not price rankings or universal recommendations.
- Before changing internal parts or cables, shut down and unplug the system as directed by its manuals.
Frequently asked questions
Does microATX reduce gaming performance?
Board size alone does not answer that. Compare the CPU, GPU, power delivery, cooling and slot operating conditions.
Does every Mini-ITX board fit every compact case?
Check case support first, then match the cooler, GPU, PSU and connector clearances.
Is a GPU short enough if it is under the case length limit?
Also check height, thickness, power-cable space and radiator interference. Some limits depend on the complete layout.
Sources and verification date
Sources checked: . These sources support the specifications, procedures or prices discussed here. Check each source for applicable conditions and current information.
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