titleWhen we got in a few oddly sized dual CPU motherboards from EVGA and Asus I posted up a few pictures on our forums and on Facebook. The problem was that even though they looked large there wasn’t any perspective. So we tossed in a couple other boards to give everyone a little perspective. This lead us to digging out even more motherboards to put together all of the standard motherboard sizes all together for everyone to be able to see the differences. Along with the picture we also have a breakdown on the dimensions of each size standard; I hope this helps everyone as some point. Sometimes it can be hard to understand all of the different motherboard sizes and how they all relate.

Write up by: Wes

Pictures by: Wes

Here is what we are talking about

motherboad sizes


Boards pictured (starting from the top left, Z format)


SSI EEB - Asus Z9P8-D8 WS

ATX - Gigabyte GA-EX58-UD4P

Mini ITX - Asus P8Z77-I Deluxe

Micro ATX - Asus P8Z77-MPro

XL-ATX - Gigabyte Assassin

E-ATX - EVGA X58 Classified


Here is a breakdown of the boards we have included in the picture. There are MANY other old and less used form factors. I would highly recommend the Computer Form Factor and ATX Wiki pages for more information on them. The measurements used below are measuring with the motherboard sitting vertical like you would have it in a tower case. Most measurements around the web will measure with the rear IO panel being down.  All of the dimensions are also listed at the MAX the standard allows.





Official Standard

Mini ITX

6.7 in

6.7 in


Micro ATX

9.6 in

9.6 in



9.6 in

12 in



13 in

12 in



13 in

12 in



10.3 in

13.5 in



15 in

13.6 in


There are a few things to point out both from the picture and the breakdown above. First you may be wondering how SSI EEB and E-ATX have the same measurements listed but in our image they are different sizes. Well the EVGA X580 Classified that we used is officially E-ATX but it doesn’t represent the maximum size possible.

 Second, like you I was curious why there would be two standards at all that have the same measurements. This is due to different standards for multi CPU and Single CPU motherboards. Specifically SSI EEB was defined by Server System Infrastructure (SSI) forum for value servers and workstations. They even go on to define the placement of each CPU to standardize cooling solutions. The real word difference between SSI EEB and E-ATX to you and I is found in the standoffs. The boards do share many of the same standoffs but there are three standoffs in the middle that do not line up. A few slight modifications and you can fit your new dual CPU SSI EEB board in your standard case.

You will also notice that I pointed out sizes that are official standards. It’s hard to not talk about motherboard sizes without mentioning that XL-ATX and HPTX are actually not official standards. Because of this finding cases that will actually fit these boards can be very difficult. XL-ATX motherboards can be found from both Gigabyte and EVGA. HPTX on the other hand was a form factor that EVGA came out with for their SR-2 motherboard and carried on with the new SR-X as well.

I hope this short write up has helped you understand motherboard sizing a little better. As always, please feel free to respond with any questions you have or with anything we might have missed. We are always happy to edit and adjust as needed to make sure we are giving you the best information. 

Author Bio
Author: garfi3ldWebsite: http://lanoc.org
You might call him obsessed or just a hardcore geek. Wes's obsession with gaming hardware and gadgets isn't anything new, he could be found taking things apart even as a child. When not poking around in PC's he can be found playing League of Legends, Awesomenauts, or Civilization 5 or watching a wide variety of TV shows and Movies. A car guy at heart, the same things that draw him into tweaking cars apply when building good looking fast computers. If you are interested in writing for Wes here at LanOC you can reach out to him directly using our contact form.

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garfi3ld replied the topic: #25182 17 May 2012 01:31
Just a little info for everyone today :)
Taino19xx replied the topic: #28505 28 Nov 2012 05:48
Thanks for the pic. Nice to have them all in one place.

Is there a relationship between mobo size and heat generated in a case (all other things held generally equal)? In particular I am trying to determine if an SSI EEB board would be any easier to cool that an ATX format.

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