TechRadar outlines the differences between different motherboard sizes and their different features and functionality ...
The typical size of an ATX motherboard is about 9.6" x 12". EATX: 13" x 12" -- A fully-featured ATX motherboard with an extended width of 13" and height of 12" instead of ATX's maximum of 12" x 9. ...
including the typical around-10.6-inch-deep enthusiast models that sometimes get tagged with today's semi-imprecise Extended ...