That's what I do - just let it grow until I can't stand it anymore, then have it cut off.
Exactly! Which makes it all the more annoying when the hairdresser won't cut enough off. In some ways I suppose I can see their point: they are worried that you will be displeased with how much they have cut off and it is easier to cut a bit more than to try to make it longer. On the other hand hair grows! If it should end up a bit shorter than you wanted, you simply need to wait a little while and then it will be longer again.