Approximate (accurate to within a couple of millimeters) dimensions: width 13 3/8", left depth is 13 3/8", right depth (because of coprocessor slot bump-out) is about 13 15/16". Almost square, but bigger than EATX, which makes finding a pre-built case very difficult. The ports extend off the back of the board, of course.
This is a B2 9/01 mobo. These dimensions may not be valid for other revisions.
BTW: My A3000 desktop from 1991 still works fine 23 years later, and I have only installed the OS once, as opposed to the 75 or so Windows machines I manage at work, which are less than 8 years old and most of which have had the OS reinstalled multiple times. It's sitting on a desk right behind me as I type this, chugging away happily. Seriously, it has several HDs attached to it that are in excess of 15 years old, with no signs of imminent failure.
They just don't make'em like they used to.

Long Live Amiga!
