Chickengirl, if you are talking about the spiral plastic ones...my cock bird outgrew the size 14. By then he had become my primary breeder, and the only boy around, so I didn't put one on him. If I had he would have needed something bigger. My girls are in size 12, but they have wiggle room.
The very important thing to remember is that you MUST check their bands often. They grow much faster than you realize and it could get really tight in a hurry. When they are little, check every week and expect to change them, if I remember right, every other week. As they get older, you don't need to change quite as often, but continue to check them. Be sure they are loose enough for you to take them off NOT just loose enough for them.
I bought my spiral bands in all sizes in white. I then went to Sally's and bought fingernail polish. Whatever was in the clearance bin. I'm very frugal with stupid stuff. Remember that you can have two of the same color since one can be on the right and one on the left leg. But you will need many sizes.
Others will chime in with what they do. There are many different gizmos to use. If you get colored zip ties, you MUST check often.
Some color code to identify their parents too and their generation. I hope this helps.
If anyone has suggestions for chicks...say 0-4 weeks please let me know. They're a pain. They grow too fast.