Once I printed out the worksheet to get the measurements it went together pretty easy.
Here are the measurements for a couple sizes: (the letters correspond to the instructions)
18 months: A-12, B-6, C-18
2-3T A-20.5 B-7, C-20
4T: A-19, B-5.5, C-17
7: A-24, B-9, C-21
18" Doll: A-12.5, B-3.5, C-8.5