Public building codes typically mandate an interior handrail height of 30 to 37 inches for staircases located against a wall and 36 to 42 inches for staircases with open sides. This height allows people to easily grab the rail for stability while climbing up and down the stairs. Though stair rails may not be required in private homes, many homeowners choose to install them on interior and exterior staircases to prevent trip-and-fall accidents.
Stand on the tread of the bottom stair. The tread is the part of the stair that people step on when climbing the stairs.
Measure the distance from the bottom of the tread straight up to the top of the handrail. If a rail hasn't been installed yet, make a marking on the wall 30 to 37 inches up from the tread. You may adjust the height to match your personal comfort level if you are taller or shorter than average.
Step up to the next tread and measure the distance from the bottom of that tread to the top of the handrail. Continue moving up the stairs and measuring the distances between each tread and each handrail. Measure from the same place on each step. The distance should be consistent and between 30 and 37 inches for rails against a wall and 36 to 42 inches for open rails.
Place a level across all the wall markings to check that they make a straight line. Skip this step if a railing is already installed.