A leather jacket should fit close to your body without restricting movement. Shoulders should align with your natural shoulder line. Sleeves should hit at your wrist bone, allowing about half an inch of shirt cuff to show. The body should skim your torso without gapping when zipped, but also without pulling or creating stress lines. You should be able to comfortably layer a shirt or thin sweater underneath. Remember that leather molds slightly to your body over the first few weeks of wear.