BushwickBill said:300' from pattern altitude make your crosswind turn. OH, and by the way this is when its safe to turn back to the runway. Until then its straight ahead and aim at the smallest tree.
Fly Safe
Not all aircraft can make it back to the runway at 500 or even 700 feet AGL. If I'm on my game and have practiced the 'impossible turn' recently, I can make a 172 or a Warrior back to the departure runway at 700'. Most of the time it's 800' AGL before the attempt will become successful. If one has a high performance single, forget it, the numbers increase to 1000' or more before the turn back to the field, even the 180 turn to land on the taxiway or the grass is iffy.
I lost 6 friends on December 23, 2004 to the impossible turn. The pilot (my friend, mentor, and an excellent flight instructor) knew better, but tried it anyways.
Something my Dad told me when I was learning to drive applies to engine failures after takeoff in singles: "When crashing, aim at the softest, cheapest thing possible."
Fly SAFE!
Jedi Nein