From the 2018 International Residential Code unless otherwise indicated.
R311.7.8 - Handrails
Handrails shall be provided on at least one side of each continuous run of treads or flight with four or more risers.
R3188.8.131.52 - Height
Handrail height, measured vertically from the sloped plane adjoining the tread nosing, or finish surface of the ramp slope, shall not be less than 34 inches (864 mm) and not more than 38 inches (965 mm).