Ease refers to the difference between the size of your body and the coat. For example a jacket for a chest of 40" will actually measure 43" so a 3" ease.You can check the ease of your best fitting blazer or coat by laying it flat on a clean surface, buttoning it up, and measuring the distance from pit to pit.Our sizes are based off of actual body measurements and have a built in ease appropriate for the garment. For example a blazer has an ease of about 3 - 4" but for an overcoat the ease increases to 10" in order to have room for layering over a wool sweater and/or a jacket. The amount of ease also increases as the size does.