E-ATX, short for Extended ATX, means a motherboard that is the same 305 mm height as ATX but wider than the standard 244 mm. The figure most often quoted is 305 × 330 mm, but the name is used loosely and boards sold as E-ATX vary a good deal in width. The practical rule is to ignore the label and compare the board's stated dimensions with what your case supports. The boards we track are on the E-ATX motherboard deals page.
Cheapest E-ATX boards right now
All 22 E-ATX motherboards, with price drops and price history
What E-ATX is, and is not
Unlike ATX, Micro-ATX and Mini-ITX, E-ATX is not pinned down by one specification that every maker follows. In practice the term covers three kinds of board:
- Consumer flagship boards that are only a little wider than ATX, often by a few centimetres. Many enthusiast boards sold as E-ATX fall here.
- Full-width boards at or near 305 × 330 mm.
- Workstation and server boards built to the SSI standards: SSI-CEB at 305 × 267 mm and SSI-EEB at 305 × 330 mm. Retail listings often call these E-ATX as well.
Case makers are just as loose: one case's E-ATX support may stop well short of another's. That is why the dimensions matter and the label does not.
| Size | Dimensions | Notes |
|---|---|---|
| ATX | 305 × 244 mm | The standard full-size board |
| SSI-CEB | 305 × 267 mm | Workstation size, often listed as E-ATX |
| E-ATX as commonly quoted | 305 × 330 mm | Boards sold as E-ATX range from just over ATX width up to this |
| SSI-EEB | 305 × 330 mm | Workstation and server size |
Expansion slots and memory slots
An E-ATX board is wider than ATX, not taller, so it has the same seven expansion slot positions. The extra width does not add PCIe slots. What it adds is room to the right of the memory slots and around the processor socket, and makers spend that room in a few ways:
- Larger power delivery sections with bigger heatsinks, for processors that draw a lot of power.
- More M.2 slots, sometimes on an upright add-in card beside the memory.
- Eight memory slots on workstation boards, such as those for sTR5 Threadripper processors. Mainstream AM5 and Intel boards still have four slots at most, however wide they are, because those processors have two memory channels.
On mainstream platforms E-ATX boards are almost always on the top chipsets, such as X870E and Z890. What each board does with the space varies, so compare specifications, not sizes.
Case compatibility
This is the part to get right before you buy. A smaller board fits a larger case, not the reverse, and an E-ATX board is the largest you are likely to meet. Check three things.
- The stated support. Look in the case's specification for a maximum motherboard width in millimetres, or for a named size such as SSI-EEB. If it only says "E-ATX" with a footnote, read the footnote.
- The cable cut-outs. In a mid-tower, the extra width usually covers the rubber-grommeted holes to the right of the board tray. The board fits, but the 24-pin and SATA cables then have to come round the edge or through a gap that is partly blocked.
- The standoffs. Slightly-wide consumer boards generally use the ATX hole pattern and leave their right-hand edge unsupported past the last column of standoffs. Boards built to SSI-EEB use some hole positions an ordinary ATX case does not have. A case that lists EEB support will have them.
Full-tower cases are the safe choice. Many mid-towers take the narrower E-ATX boards, but check the figure every time.
Cooling and cable routing
The extra board area helps cooling on the board itself. Power delivery heatsinks are larger, M.2 drives are spread out, and there is generous space around the socket for a big cooler. The board does not make the rest of the PC run cooler; that is down to the case and its fans.
Cable routing is where a wide board in a marginal case causes trouble, for the reasons above. In a case designed for the size it is no harder than ATX. These boards often want more from the power supply too: two 8-pin CPU power connectors are common, and some add a further connector for the PCIe slots.
Price tendencies
E-ATX boards sit at the top of each maker's range, so they are among the most expensive boards on any platform, and workstation boards cost more again. There is no budget E-ATX. Because the starting prices are high, a percentage drop or an open-box discount is worth more in pounds here than anywhere else, and a board sent back only because it did not fit the buyer's case can be a good open-box buy. Read Are Amazon Warehouse motherboards worth it? before buying one that way.
Who should buy E-ATX
- Workstation builders on Threadripper, where most boards are this size or larger; see the sTR5 socket guide.
- Enthusiasts who want a specific flagship board for its power delivery, connectivity or overclocking features, and have a case that takes it.
Almost everyone else is better served by ATX, which runs the same processors and graphics cards at the same speed. How much to spend on a motherboard explains where extra money stops showing in use, and ATX vs Micro-ATX vs Mini-ITX covers the mainstream sizes.
What to look for when buying
- The exact dimensions in millimetres, checked against your case.
- The power connectors the board needs, checked against your power supply's cables.
- What the width is used for. If it is features you will not use, the ATX model below it is the better buy.
- On open-box boards, the bundled extras: M.2 add-in cards, aerials and cables are a real part of a flagship board's value and are easily left out of a return.
Current prices are on the E-ATX motherboard deals page, and Warehouse offers lists open-box boards of every size.
Questions people ask
What size is an E-ATX motherboard?
There is no single answer. The height is 305 mm, the same as ATX, and the width is anything over the ATX figure of 244 mm. 305 × 330 mm is the size most often quoted, but many boards sold as E-ATX are narrower than that. Always use the dimensions in the specification.
Will an E-ATX board fit my ATX case?
Only if the case says so, and only up to the width it states. Many mid-towers accept boards a little wider than ATX, usually at the cost of covering the cable cut-outs. Check the maximum motherboard width the case lists against the dimensions of the board.
Does E-ATX have more PCIe slots than ATX?
No. The board is wider, not taller, so it has the same seven slot positions. The extra space goes on power delivery, M.2 slots, extra features and, on workstation boards, more memory slots.
Is E-ATX better for gaming?
Not because of its size. A good ATX board runs the same processor and graphics card just as fast. E-ATX boards are flagship models, and what you pay for is features and overclocking headroom, not frame rate.