Righty ho.
Last time I bought a Mountain Biking jersey, short-sleeved; I think I had the only MTB jersey but these are looser around the waist/hips which is a good thing (a) for a recumbenteer, so you can cover your belly; (
for a lady, as men's hips are too narrow so normal jerseys are too tight around my ladylike shape.
But I shall be kind and do some measurements for you.
Mine was a Large (L) - what can I say, I'm an ample lady!
Armpit to armpit (laid flat) 61cm or 24"
Length from collar to bottom - 76cm or 30"
Round the neck - 46cm or 18"
This fitted me well when I was a size 18 but is now a bit too large as I'm a size 16.