Proper sleeve length is right or wrong ... or falls within the acceptable zone. In this video men's style, grooming, fitness and lifestyle expert, Aaron Marino of IAmAlphaM, AaronMarino, and Pete & Pedro says that the detail that can foul up your entire outfit is not handling your sleeve length. Too long looks like your jacket was not tailored and too short looks like you outgrew it. If you nail it, perfection!
Alpha demonstrates where your cuff should fall. He explains what happens if it doesn't fit. With made to measure shirts, you can precisely pick where you want that button. You can also take off and sew the button in the proper place.
Make sure the sleeve hits the wrist bone. The difference between the shirt and that bone is 1/2 inch. That's how much cuff should show. Alpha demonstrates too long and too short, which he recommends a trip to the tailor.
When buying a jacket, you need to make sure the jacket fits as close as possible in the sleeves because you can only adjust the sleeve length 'so much' (1/2 inch let out; take up 3/4 - 1 inch max). You can also have the jacket sleeve off and move arm up, but a professional touch is needed.