This measurement is of the armwarmers lying down flat and does not give an idea of how far the arm warmers will stretch. I got the upper opening to stretch to 350mm without maxing it out so the arm warmers will fit a wide range of arm sizes.

There is sizing information under the description tab.

I am ever so sorry to post my reply. It could be the christmas spirit or it could be the dirt I am covered in havinf returned from my local tracks after a night ride of awesome grit (pretty tame but a bit muddier than usual so oooo...slipped a bit into a few corners). I just wanted to answer your question with a question. Does it matter? THe real question is do they work and the answer is yes, they work. THey keep you warmer and they fit pretty well but I have always found a god windproof more adaptable. If you unzip it keeps you cool when riding and it works when you get a puncture. Having been caught out above Grisedale in January 5 years ago I swore I would never be caught out by puncture chill again. For racing on road, try them. For other uses, get a front zip. Hope this helps and Merry Christmas!

The sizes we have in stock now are the only ones left the rest have been discontinued.