Jerseys, jackets and vests are sized by chest measurements, but within a given size the fit can be quite different. Each jersey or jacket is tailored for a specific type of rider.
There are 3 types of fit: The casual rider who is most comfortable in a loose, generously fitting jersey will want to look for a garment described as Loose, Relaxed or sometimes as a Club Fit. The serious rider who wants a jersey that does not flap in the wind but stills gives him plenty of room will want the slightly tighter and more tailored jersey or jacket usually termed Semi-form fit. The serious racer will want the more fitted and closest fitting garment described as Form Fit, Race Fit or Euro fit.