Most are less than 2' x 4'. You'd want about a foot of clearance on both sides, too, just so you don't feel too claustrophobic, but you could probably do with 6" if you had to.
Not big enough to stop me from getting one, hehe. I put mine in the corner of my bedroom and it has wheels on one side for tilting so it's so easy to move it into the family room when I want to spin. The footprint on mine is 40" X 20" Proform. The handles bars stick out a little further than the feet so it's more like a 45" X 20" for storage.