How do doctors decide which size needle to use when stitching a wound?

Soft skin = small: The more delicate the skin, the finer the thread and therefore the finer the needle that is required. The needles/thread range from 1 to 6 (largest to smallest). Generally for the face we use a 5 or 6, for the arms and hands a 4 and for the legs a 3 or sometimes a 2. Size 1 is for heavy duty jobs like holding a piece of surgical tubing in place.