This Jacket Size Reference gives you description of standard sizes. Look at the item description for any deviation from this standard.
Sizes for Jackets, Coats & Vests
SIZE
 MEN'S LADIES

S
M
L
XL

 38"-40" Chest
40"-42" Chest
42"-44" Chest
44"-46" Chest

32"-34" Chest 36" Bust - 6-8
 34"-36" Chest 38" Bust - 8-10
36"-38" Chest 40" Bust - 10-12
38"-40" Chest 42" Bust - 14-16