What is the differences between US shoe sizes and UK shoe sizes?

The male shoe sizes USA are generally a half size smaller that Male UK i.e. USA 2 = UK 2.5. US 5.5 = UK 6

Female are somewhat less conventional

Ladies US shoe Size is 2.5 sizes bigger than UK ladies i.e US 5 = UK 2.5, US 7 = UK 4.5

UK Girls shoes are half size smaller than US size i.e US 8.5 = UK 8

Strange but that's it.