The Short Answer
A bathroom mirror should generally be the same width as the vanity, or 2-4 inches narrower on each side. For a 48-inch vanity, a 40-44 inch mirror is appropriate. For a 60-inch double vanity, two separate mirrors are often preferable to a single large mirror. Height: most bathroom mirrors are 24-36 inches tall. The bottom of the mirror should be 5-7 inches above the faucet. The top should be at or near eye level for the tallest user or slightly above.