Most of the range uses single sizes — M, L, XL and up to 5XL. Some knit sets are cut differently and come in pairs: S-M, M-L, L-XL, XL-2XL, 2XL-3XL. That is not a shortcut; it is how the garment is made.
What a pair covers
Knit stretches. A piece cut for the S-M range is made to sit well on a man who wears S and on a man who wears M, with the difference taken up by the knit rather than by a separate pattern. Each pair covers exactly the two sizes it names.
If you sit between the two
Take the pair that contains your usual size. If you wear M, both S-M and M-L will fit — S-M will sit closer, M-L will sit easier. Pick by how you like knitwear to sit, not by the letter alone.
Where the numbers are
Every product page carries a size chart for that specific piece, with a height and weight guide per size and a calculator that suggests a size from your measurements. Those figures describe the garment, so compare them against something you already own and like the fit of.
Trousers are separate: they are sold by waist in inches — 29 through 36, and 38 upward on some cuts.
