Very roughly, 28" x 26". For this thing:
The front is about two inches narrower than the rear. The cabinet is probably about 1/8" thick steel, with the base bent 90? to form a lip of about an inch all around the inside perimeter. Works fine when the whole thing is resting on the floor, but other owners who have mounted casters to their machines have advised that the front lip cannot take the weight and tends to bend inwards without being reinforced. I'm not brave enough to weld a piece of channel to it and void the warranty yet.