Answer:
This varies depending on many factors. The aircraft's weight being foremost, a heavily loaded 172 can require as much as 3 times the runway as a nearly empty one. Additionally outside air temperature makes a big difference. On a hot day, you may need 200 to 500 feet more runway, and may not be able to take off at all if youre heavy. Field elevation plays a big role as well, some airports may be more than 5000 feet above sea level, this means less lift from your wings, and more runway. Weather can help or hurt you. A good stiff headwind might save you 200 or 300 feet from your takeoff roll, but its just as likely youll get a crosswind which may cost you. Pavement makes a huge difference, taking off from grass ususally takes at least 100 feet more runway.
Bearing all that in mind, on a nice summer day, with just me in the plane & about a half-tank of gas, i can easily get off the ground in under 800 feet of runway, and if im trying, as little as 500.