The United States Occupational Safety & Health Administration sets the handrail height requirements for building new handrails on stairs at between 30 and 37 inches. OSHA requirements apply to most private sector and governmental employers in the United States.
To take this measurement, place a measuring tape or other measuring device at the corner edge of the step, where the tread meets the riser, and then measure straight upwards, parallel with the riser, to the top of the handrail surface. If the stairs have a stair rail that is between 36 and 37 inches from the top surface of the stair rail to the surface of the tread, the stair rail can serve in place of a handrail. If the stair rail does not fit these measurements, a separate hand rail is necessary.