6.75 feet, haha. It depends on the length of the rail. you're gonna want 10-15 feet to get up and plane and at least like 10+ feet to land. With say a 10 foot rail, you may want like a 35ft- 40ft pool... Why?
my backyard has got a 65 foot area where i was thinking of putting it somehow. I was thinking about 4 feet of a starting platform, and a 10-15 foot rail. im not to sure it would work out.