The point: This is absolutely, positively how a blazer or suit jacket arm length should be tailored. Period. (And how much cuff to show on a dress shirt under it.)
Here are the keys:
- Your shirt cuff should meet the break of your wrist when your arm is straight by your side in a comfortable position (NOT to be confused with how to measure yourself for a shirt sleeve- i.e., crooked elbow, shoulder to wrist).
- You should show 1/4 to 1/2 inch of cuff before your jacket begins (again, same position- arms by your sides).
- Caveat: You will notice when you bend your arms (e.g., while driving) you may see your wrist and the jacket may seem higher up your forearm than you are used to. But this spec is still the difference from being well-dressed versus being stylish.
*Side note: I have a dress shirt on right now given to me as a gift and it is not my customary brand/sizing, but a close facsimile; It is driving me nuts because, despite the shirt stating the same measurements, the sleeves are juuuust a bit longer than my usual measurement and it is driving me crazy! (Yup, I have issues.)