Size down, way down
I typically take a m or a l in retailer tops/sweaters, so i ordered one of each, as this has been on back-order for forever. the medium was swimming on me - and i have a very athletic frame, with huge traps and biceps. i could have easily taken this in a small and still had plenty of length in the sleeves - and i have very long arms. 
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this sweater is thick and heavy. there's no way here in atlanta it can be worn anytime other than spring and the occasional very, very cool summer night.