House address numbers should be at least 5 inches high, although those on existing residences can be 3 1/2 inches high. Many cities have laws stipulating the size and sometimes the color of house address numbers.
House numbers that can be seen clearly from the street make it easier for paramedics, police and firemen to quickly locate the property in the event of an emergency. Reflective numbers are preferred because they are easier to see at night.
The house numbers should be placed clear of any shrubs or trees that may obscure view from the street. The best place to position the numbers is on the front door if it is visible from the street, or on a tree, fence or post at the driveway entrance if not.