You aren't. I don't have the exact measurement for them. They generally fit 0-6 months but if you need one bigger, I can make a bigger one or a teeny one if you need it smaller for a preemie.
I can have the winner take a head measurement and if the size isn't right, I can make it bigger or smaller. I made all of these and have plenty of leftover supplies. I can also take them off the headband and put them on a clip instead if someone has a baby with more hair....or a bigger child.