Buffalo plaid jacket size small / medium faux leather coat

Buffalo plaid with faux leather arms and trim In good clean well cared for condition Designed by Red snap Form fitting Tag says medium but I feel like it measures more like a small , especially if you were to wear a sweater under it Please compare my measurements to yours for best fit Measuring approximately laid flat 18 pit to pit 21 shoulder to hem Sleeves 18 pit to cuff