XS    S   M   L XL
PTP
15" 16" 17" 18" 19"
Waist 12" 13" 14" 15" 16"
Hip 17" 18" 19" 20" 21"
Length 32.5" 33" 33.5" 34" 34.5"

*Model is 1.70m, UK 4/6 (PTP15", Waist 11.5", Hips 16.5") wears size XS

If you are in between sizes for PTP, it is best recommended to size up. 
If you are in between sizes for waist, it is best recommended to size up. 

*In between sizes refers to your measurements falling between 2 sizes, example size S & M.