Stair Handrail Length Calculator
Handrail length for a staircase from the number of risers, riser height and tread depth: sloped length, code extensions, stair angle, stock length, brackets and handrail height.
How it works
sloped length = (risers − 1) × √(tread² + riser²) · commercial/ADA: + 30 cm (12″) level at the top + one tread depth at the slope at the bottom · angle = atan(riser ÷ tread)
A stair handrail runs parallel to the nosing line from directly above the top riser to directly above the bottom riser, so its sloped length is the number of tread spaces (risers − 1) times the diagonal of one step. The International Residential Code (R311.7.8) requires a handrail on at least one side of any flight with four or more risers, 34–38″ (86–97 cm) above the nosings and continuous for the full flight. Commercial and accessible stairs under the IBC (1014.6) and the 2010 ADA Standards (505.10) also need a 12″ (30 cm) level extension at the top and an extension of one tread depth at the slope at the bottom. Brackets go at most about 1.2 m (4 ft) apart.
Worked example
14 risers of 18 cm with 28 cm treads: one step’s diagonal is √(28² + 18²) = 33.3 cm, and the rail spans 13 of them, 13 × 33.3 = 4.33 m, at a stair angle of 32.7°. A residential rail needs no extensions, so buy one 4.88 m length per side and 5 brackets, and fix it 86–97 cm above the nosings.
Sources: ICC — 2021 IRC R311.7.8 Handrails · US Access Board — 2010 ADA Standards 505 Handrails
Frequently asked questions
How do I calculate the length of a stair handrail?
Multiply the number of risers minus one by the diagonal of one step, √(tread² + riser²). For 14 risers of 18 cm and 28 cm treads that is 13 × 33.3 cm ≈ 4.33 m. Add the code extensions for commercial or accessible stairs and a little for end returns.
What height should a stair handrail be?
Between 34 and 38 inches (86–97 cm) measured vertically from the line of the tread nosings to the top of the rail, in both the IRC and IBC.
When is a handrail required on stairs?
Under the IRC, any stair with four or more risers needs a handrail on at least one side. Commercial stairs under the IBC generally need handrails on both sides.
How far apart should handrail brackets be?
Most manufacturers specify brackets no more than 4 ft (1.2 m) apart and within about 12″ (30 cm) of each end, fixed into studs or blocking.
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