Where the sleeve should end on the arm
Short answer: A short sleeve ends midway down the upper arm, a long sleeve at the wrist bone. Anything else is a style choice rather than a fault.
The short sleeve
On an ordinary t-shirt the sleeve ends roughly halfway between shoulder and elbow. Ending higher makes the arm look longer. Ending at the elbow makes it look shorter. Both work, but they do different things.
The long sleeve
A long sleeve should end at the bone that sticks out at the wrist. If it covers half the hand, the garment is too big or the cut too long. See long sleeve bamboo tops for men.
Sleeve width counts too
A sleeve that is wide at the upper arm makes the arm look slimmer, but the fabric folds under a jacket. A tight one is noticeable when you bend the elbow. See long sleeve bamboo tops for women.
When the sleeve rides up
A sleeve with no ribbed cuff rides up when you bend your arm. Choose a style with a ribbed cuff if you want it to stay. See bamboo sweatshirts for men.
Frequently asked questions
Can a sleeve be shortened at home
On knitted fabric it needs a stretchy seam. An alterations shop does it quickly and cheaply.
Should a three quarter sleeve cover the elbow
No. A three quarter sleeve ends between elbow and wrist and leaves the wrist visible.
Why are sleeves different on two garments in the same size
Because sleeve length is its own measurement that each brand sets for itself.