Handrail Length Calculator
Calculate the handrail length needed for a staircase from the horizontal run and vertical rise.
Supports imperial and metric.
A handrail must meet building code requirements for safety, and calculating the correct total length and post spacing is essential before purchasing materials. The formula depends on the staircase’s total rise, total run, and the required post intervals.
Stair geometry: Stair Angle = arctan(Total Rise / Total Run) Stair Length (hypotenuse) = √(Total Rise² + Total Run²)
This stair length is the actual handrail run along the slope.
Post spacing: Building codes (IRC R311.7.8) typically require balusters no more than 4 inches apart (so a 4" sphere cannot pass through). Posts (newel posts) are typically spaced every 72–108 inches (6–9 ft) depending on structural requirements.
Number of Posts = Ceiling(Stair Length / Max Post Spacing) + 1 Actual Post Spacing = Stair Length / (Number of Posts − 1)
Worked example: Staircase: Total Rise = 9 ft, Total Run = 12 ft Stair Length = √(9² + 12²) = √(81 + 144) = √225 = 15 ft At max 8 ft post spacing: Posts needed = Ceiling(15/8) + 1 = 2 + 1 = 3 posts Actual spacing = 15 / 2 = 7.5 ft between posts Handrail length = 15 ft + 1 ft (overhang each end) = ~17 ft
Code requirements (IRC 2021):
- Handrail height: 34–38 inches above stair nosing
- Required when staircase has 4 or more risers
- Graspability: diameter 1.25–2 inches for round rails; grip zone profile required for other shapes
- Ends must return to wall or newel post (no protruding ends)
Material lengths: Standard handrail stock comes in 8 ft and 12 ft lengths. Order 10% extra for waste cuts at angle.