heres my formula
25 inches=4 inch bow
30in=5 inch bow
36in=6 inch bow
42in=7 inch bow
All my tails are 1inch.
I do mine by hand also not with a gatorbite or bowmaker. Not sure if that helps or not. But I'd say for a 9 yr old go with 5 inch or bigger. I did a order of 10 bows and make them all about 6 inchs for her (she's a tweener) and the mom is now ordering 10 more and said she loved them!
I guess its the new craze, she said her daughter wont even tell her friends where she got them from, so that way they won't have cute bows like her!
While that was flattering I would love more biz!!!...lol