Are All Motherboards The Same Size? | Form Factor Tips

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No, motherboards come in multiple form factors—ATX, Micro‑ATX, Mini‑ITX, and E‑ATX—with fixed dimensions and matching case requirements.

Shopping for parts can raise a simple question: are all motherboards the same size? Short answer—no. Size follows the form factor, which sets board dimensions, standoff locations, and how the rear I/O lines up with the case. Pick the wrong pair and the build stalls. Pick the right pair and everything clicks.

Are Motherboards The Same Size? Form Factor Variants

Desktop boards come in a handful of common sizes with set width and length. Here are the ones you’ll meet most often:

  • Mini‑ITX: 170 × 170 mm (about 6.7 × 6.7 in).
  • Micro‑ATX: 244 × 244 mm (about 9.6 × 9.6 in).
  • ATX: 305 × 244 mm (about 12 × 9.6 in).
  • E‑ATX: up to 305 × 330 mm (about 12 × 13 in), width varies by maker.

Each size maps to a matching case class. A mid‑tower usually handles ATX and smaller. A compact case targets Mini‑ITX. Many full towers leave room for wider E‑ATX boards. Check the case spec sheet for the exact list of board sizes it fits.

Why Size Matters For Compatibility

Form factor is more than a rectangle. It dictates how the board mounts, where headers sit, and how much clearance parts get. Here’s what changes with size:

  • Mounting pattern: The standoff map—the grid of screw points—differs by size. Correct posts prevent flex and shorts.
  • Rear I/O alignment: ATX‑based layouts place USB, audio, and video in a standard I/O shield area. Cases built for that layout line up cleanly.
  • Expansion room: Longer or wider boards allow more PCIe slots and M.2 locations. Tiny boards trade count for compact builds.
  • Memory slots: ATX often gives four DIMM slots. Micro‑ATX frequently gives two or four. Mini‑ITX almost always ships with two.
  • Cooler and GPU clearance: Small cases matched to Mini‑ITX leave less headroom for tall air coolers or long graphics cards.
  • Connectors: Fan headers, front‑panel pins, USB headers, and SATA ports share tighter real estate on small boards, which can affect cable runs.

In short, size drives fit and features. Once you lock the case, the board size follows. Or pick the board first and choose a case that matches—both paths work.

ATX, Micro‑ATX, Mini‑ITX: What Changes As You Shrink

All three are based on the ATX layout for I/O placement, so cables and shields land where you expect. The big differences land in slot count, header count, and working room inside the case.

ATX: Full‑Size Flexibility

ATX boards stretch to 305 × 244 mm, which opens room for more slots and features. Many ATX models offer:

  • Three or more PCIe slots for add‑in cards.
  • Four DIMM slots for memory capacity without high‑density sticks.
  • Two to four M.2 sockets plus several SATA ports.
  • Heatsinks with a bit more mass and space for VRM cooling.

This size lines up with mid‑tower and full‑tower cases. Cable routing holes and grommets usually clear the edge of an ATX board, which keeps cable runs tidy.

Micro‑ATX: Balanced Builds

Micro‑ATX trims the length to 244 mm while keeping the same width as ATX. Many mATX boards still carry a full‑length PCIe x16 slot plus one or two shorter slots. You often keep two or four DIMM slots, one or two M.2 sockets, and enough headers for a couple of case fans. The footprint fits a wide range of compact mid‑towers.

Mini‑ITX: Small And Focused

Mini‑ITX boards measure 170 × 170 mm. You get two DIMM slots and a single full‑length PCIe slot in most models. Storage tends to be one or two M.2 sockets and a couple of SATA ports. Builders pick Mini‑ITX for tiny cases, clean desk setups, or travel rigs. Cable reach and airflow planning matter more because space runs tight.

For the nuts‑and‑bolts rules behind ATX and Mini‑ITX sizing, see the official design guides. The ATX Specification v2.2 lists ATX board size and mounting points, and Intel’s Thin Mini‑ITX design guide shows slim variant mechanical limits and keep‑out zones.

E‑ATX, SSI, And Oddballs: When Larger Boards Make Sense

E‑ATX widens the board past the 244 mm ATX width. The common upper bound lands near 330 mm, though some retail “E‑ATX” boards sit a few millimeters short of that. The extra width creates room for more M.2 sockets, beefier heatsinks, and more space between slots. Workstation boards based on SSI‑EEB or similar layouts also live in this class. Many gaming and creator cases accept one of these wide boards, but cable grommets or radiator mounts can clash with the edge of the PCB. Check the case spec page and note any callouts about grommets or radiator conflicts.

One more wrinkle: case brands and board brands don’t agree on a single, fixed number for E‑ATX. A case marked “E‑ATX ready” might fit a 305 × 330 mm slab, or only a 305 × 277 mm board. Always look for the actual maximum width in millimeters and compare it to the board page.

Picking A Case For Your Motherboard Size

Match the case to the board, not the other way around. Read the case spec table, then cross‑check the board page. Aim for clean cable paths, fan placement that fits your plan, and room for the cooler and graphics card you want. Here’s a quick checklist:

  • Size line on the case page: Look for the exact list of form factors (Mini‑ITX, Micro‑ATX, ATX, E‑ATX) and the maximum width in millimeters.
  • Standoff map: Many cases ship with posts pre‑installed for ATX. Move or remove posts for Micro‑ATX or Mini‑ITX so they align with the board holes.
  • Cable grommet placement: Wide E‑ATX boards can block the nearest pass‑through holes. If that happens, route behind a lower cutout or use a 90‑degree adapter where possible.
  • Radiator and air cooler limits: Check top, front, and rear clearances. Taller air coolers and thick radiators need space above the motherboard edge.
  • GPU length and thickness: Small cases around Mini‑ITX often cap length and slot count. Measure the card against the case spec before you commit.
  • Front‑panel reach: Power switch, LEDs, USB, and audio cables must reach their headers. Short runs in tiny cases can get tight once the PSU and GPU go in.

Building around Mini‑ITX? Slim system guides show how cable paths and keep‑out zones shape the layout; the same planning helps many compact builds.

Cooling, Power, And Cable Fit By Form Factor

Thermals And Airflow

Smaller cases mean tighter air paths. Plan intake and exhaust so air passes across the GPU and CPU cooler without dead zones. Builders often aim for two front intakes and one rear exhaust on compact towers. In SFF enclosures, a side or top intake near the GPU helps a lot.

VRM And Heatsinks

Board size can affect power stage area and heatsink mass. Many Mini‑ITX boards run fine at stock settings, but heavy overclocks push heat into a tight space. A case with clear top ventilation and a direct path over the socket gives better results.

PSU Types And Fit

ATX cases often take standard ATX PSUs. Compact cases might need SFX or SFX‑L units to make room for cables and a GPU. Check PSU length against the case spec so the front fan or radiator still fits.

Cable Management

More space makes tidy routing easier. Full towers often hide the 24‑pin and EPS leads behind grommets. In Mini‑ITX cases, plan the order: install the backplate, run front‑panel cables, seat the cooler, then slide in the GPU last.

Common Build Mistakes And Fixes

  • Wrong standoffs: Extra posts under the board can short traces. Match the case posts to the board’s hole pattern before you tighten screws.
  • E‑ATX in a mid‑tower: The board might block cable cutouts or bump into a front radiator. Double‑check maximum board width on the case page.
  • Mini‑ITX with a tall air cooler: Many cube or sandwich‑layout cases cap cooler height. Pick a low‑profile air cooler or a slim AIO that clears RAM and side panels.
  • GPU length math: Specs often quote max length without front fans. Subtract fan thickness to get the real allowance.
  • Short front‑panel leads: Some compact cases ship short cables. Extensions exist for USB 3 header and HD‑audio leads if you come up a few centimeters short.
  • Blocked M.2 slots: On some boards the primary M.2 sits under the GPU. A heatsink with a backplate or a riser can help temps, or use an alternate slot if the board has one.

Quick Reference: Motherboard Form Factors And Dimensions

These numbers match the common consumer sizes. Check the product page for exact figures and mounting maps.

Form Factor Dimensions (mm) Typical Case Fit
Mini‑ITX 170 × 170 Mini‑ITX, some Micro‑ATX towers
Micro‑ATX 244 × 244 Micro‑ATX and most ATX towers
ATX 305 × 244 ATX mid‑towers and full towers
E‑ATX Up to 305 × 330 Full towers marked E‑ATX capable

Buying Advice: Which Size Should You Pick?

Small Desk, Clean Look

Go Mini‑ITX with a compact case that takes a short GPU and either a low‑profile air cooler or a 240 mm AIO. Pick two 24‑ or 32‑GB DIMMs for easy capacity. Aim for a PSU length that leaves space for front fans.

Mainstream Gaming Or Daily Work

Micro‑ATX lands in a sweet spot. You keep room for a graphics card, two to four memory slots, and enough storage without a cramped layout. The case can be smaller than a full ATX tower, yet airflow stays straightforward.

High‑End Gaming Or Creator Workloads

ATX or a wider board fits better here. You get more M.2 sockets, extra headers, and cleaner cable paths. A larger case also leaves room for a taller air cooler or a thick front radiator, plus space around the GPU for airflow.

Pre‑Build Checklist

  • Confirm the board form factor and dimensions in millimeters.
  • Read the case spec table for maximum board width and the list of form factors it fits.
  • Lay out the standoff pattern before the first screw.
  • Measure cooler height, radiator thickness, and GPU length with fans installed.
  • Plan cable runs for 24‑pin, EPS, GPU power, front‑panel, and USB headers.

Final Takeaway

Motherboards are not the same size, and that’s by design. Pick a form factor that matches your case and goals, and the build goes smoother. Start with the board and case pairing, check clearances with the parts you already own, and you’ll avoid the common fit gotchas above.