Once you’ve narrowed in on a style, the next thing to consider is the fit. First, think about how you intend to wear the jacket. If you prefer to wear it unzipped, you may want to go for a smaller size to avoid looking like you're wearing a garbage bag. If you would rather layer your jacket over sweaters, you might want to size up.
When you’re trying on a jacket, the sleeves of your jacket should not extend past the wrists. If you’re sporting one of the four classic styles, the jacket should sit at your waist. Those are the basics, but there are two more quick tests to perform to make sure the jacket is a good fit.
First, is the "stuck test. Hold your arms above your head. The jacket shouldn’t feel tight as if you’re “stuck” in it. The jacket also shouldn't ride up past your waist. Next is the "finger widths test." Simply place two fingers under the bottom hem of the jacket. Make sure there's enough room to slide your fingers between the jacket and your body.
The jacket should also be comfortable around your arms with close-fitting arm holes. Even if you find it more comfortable, hanging armholes will make the jacket look ill-fitting. While you're checking the armholes, make sure the jacket isn't too tight around your chest. If your chest and shoulders are much wider than your waist, look for jackets with diagonal zippers. These may fit better.
The shoulder fit is the most important. Make sure the jacket lays flat against your shoulders. Again, make sure that nothing feels "stuck" or too tight. Leather is difficult and expensive to tailor, so be sure the fit is perfect before you make a purchase. An easier way to ensure your jacket fits perfectly is to simply buy a custom leather jacket, however the cost is typically higher and you have to make sure you do your measurements correctly.