As you know sizing differs not only from country to country, but also by designer. In order to simplify things, Derek Rose have interpreted the various sizes into a standard S, M, L, XL & 2XL system.
The table below outlines the conversion into waist size (Inches)
S | M | L | XL | 2XL |
30-31 | 32-34 | 35-37 | 38-40 | 41-43 |