It is always advisable to check out riding gear in person, be it jackets, pants or boots. Different jackets in the same chest size fit differently depending on the type of materials, amount of padding, detachable lining/armor and the like.
If you buy without trying, there is always a chance that it is too tight for you, or it can make you look a saggy poweranger
If you are still bent on buying it online, make sure the exchange policy is clear.