I don't know of a chart off-hand, but just play around with it and you can create a template for yourself according to the way you like them to look.
And I know there are some general headband sizes that girls have posted. Up at the top, there is a search function, you could try searching "stretchy headband sizes" or something and see if it comes up. Also, alot of sellers on etsy will list a headband size chart so you could check that out too. HTH!