House numbers The best size Bigger is better. The number should be at least four inches tall if displayed on a house or street curb. On a mailbox, no less than three inches tall. Get boldface type. Thick and wide is better. Mailbox. Show only your number. We don't need your name and street. Don't get small numbers and cram all that information on the side of your little mailbox. Only your house number please! Last updated: August 4, 2008