Measuring a man's suit

[msemma]

How can I tell what size a man's suit is to put it on Ebay? I know my partner's size and it's too big for him! How can I measure the size of the jacket? Where to I measure it from? Across the shoulders at the back? On the inside? Arm length? Confused!

[spudqueen]

Is there a label inside (maybe inside the seam not at the back of the neck) with the size on? If not I would measure across the back of the jacket at the bottom of the arms, then maybe inside arm length (from the armhole seam to the cuff). Do state where you took the measurements from.