I really like this shirt jacket. I was concerned about what size to order and the very nice woman who answered went to grab one and take measurements while I was on the phone and offered to swap it out no questions asked if it didn't fit right.
I'm 6' 190lbs with a 44" chest and usually wear a 42 regular suit. The medium fits just right. Being in SC this is a 3+ season item. The only change I'd make is to take the lining that's just at the cuffs and run it up the whole sleave. I wear it over a short sleeve shirt a lot and the liner would just make it more comfortable vs the wool on my arms. No regrets on this purchase.