A winter jacket should fit snugly without being too tight. If the coat is too small, the down might become compressed and less effective, plus your mobility will be restricted. You’ll know it’s too tight if you can’t easily give yourself a hug, arms touching your shoulder blades. The jacket should never rise above your belly, and the shoulder seams should not be resting mid-bicep. Feel free to size up in winter jackets, especially if you plan on layering, but make sure you can still perform daily activities without the bulk of the coat getting in the way.