What cases can I buy for my motherboard?

It should fit in any case that supports the ATX form factor. The size isn’t so much an issue as where the holes are to mount it to the case and every case I’ve seen has multiple places for the screws to go into.

Out of all the computers I’ve built I’ve never looked at the size measurement.

If the board says ATX and the case says ATX, then they are compatible. Just remember that there are, in fact, very tiny cases that will only hold a certain size of board (ATX boards range from Micro to Mini to just ATX), so make sure the case you have can fit it. Most will, of course. Go ahead and link us the case if you know what it is.

Also, I’m curious to know the application for the build if you’re using an AM2 socket processor…

By definition, as laid out in ATX Form Factor Specification v 2.2, ATX motherboards are 12.000” x 9.600”. There are similar specifications laid out for related form factors such as Mini-ATX, MicroATX, FlexATX, and others, but those do not concern you.

All you need to know is that all ATX mobos are 12“x9.6”, any case that is listed as ATX conforms to ATX standards and thus will accept any ATX Motherboard (though it may be too small to allow certain add-on cards, such as your larger video cards), and that the ATX form factor is the most widely used; most mobos and cases ont eh market now are ATX.

I share @Fred931‘s curiosity as to what this build is for, since AM2 is deprecated five years ago.

@mrentropy Your experience should tell you how ubiquitous ATX is; you have to look for stuff that is not ATX. And yes, ATX Spec v2.2 also specifies screw locations.