This is usually what GP supplies and there is more than enough. You'll need about 21 hinges total (3 per surface - 4 ailerons, 2 elevators, 1 rudder) and If I'm not mistaken, they give you 2 sheets.

You really don't even have to measure anything. Just cut the strip in half lengthwise, then lay one half on top of the other and cut strips that are about 3/4 of the width.

These things are very strong, so if you're off by a little bit it's not going to hurt anything