US 

UK

 Length (cm.)
4 2 21
4.5 2.5 21.6
5 3 21.9
5.5 3.5 22.2
6 4 22.9
6.5 4.5 23.2
7 5 23.5
7.5 5.5 24.1
8 6 24.4
8.5 6.5 24.8
9 7 25.4
9.5 7.5 25.7
10 8 26
10.5 8.5 26.7
11 9 27
11.5 9.5 27.3
12 10 27.9
13 11 28.4