The first jacket I received had symmetry issues, so I exchanged (customer service is excellent). I ordered size medium which I felt was a bit snug, especially in the arms. For context, I am 5'10, 173 ( I fluctuate between 170-175), 16" neck, 41 sport jacket, 34" arms, 33" waist. I consider myself between a medium to athletic frame. I considered a large, but after speaking to customer service, I decided to keep the jacket and break it in. It's slowly loosening up. Since this is rated to 1°, you can wear a light sweater and stoll be warm. FYI, I tried a medium short as suggested by customer service, and it was way too short for me, including in the sleeves. Hope this helps you decide. PS, it is a heavy jacket, but it doesn't bother me.