The maximum lenght your'll get into a standard size garage is about 4.8 metres, and this all depends on the draw bar at the front, worth also remembering the width of the boat too as a wider boat might mean having to deflate the tubes to get it in, its not the garage size really but the width and height of the door.
I had my A frame made lower to specifically fit under a standard 6' garage door, with ariels and gps antenna it just slips under.
One of the sales points for the Ribcraft 4.8 is that it fits into a garage !!!
Good luck and enjoy the buying process