What are the standard sizes for necklaces, in particular for men? How big should bracelets be?
Necklace lengths are given in standard inches for both men and women. Men's styles tend to rest close to the neck. Most of the men I know are wearing styles from 18 to 20 inches long, depending on the size of their necks.
Bracelet lengths are determined by the size of the wrist they're going on. Most women's wrists accommodate a 7-inch to 8-1/2 inch chain, although some require either shorter or longer styles. Men commonly require bracelets (or watchbands) at a minimum of 9 inches long, although some may need larger sizes.
Your best bet is to measure first, then create to fit.