Handrail Length Calculator
Get the handrail length for your stairs — the sloped grip run plus the code-required top and bottom extensions — with mounting height and grip diameter checked against your building code.
Handrail height and where a rail is required come from this jurisdiction.
Finished floor to finished floor.
There is one fewer tread than risers, so the run spans 15 treads.
The horizontal depth of one tread; sets the bottom extension.
Top of the rail above the stair nosings.
Total handrail length
19' 7 15/16"
5.993 m
Sloped grip length
16' 8 15/16"
5.104 m
Pitch
34.9°
Top extension
12"
305 mm
Bottom extension
23"
584 mm
Mounting band
34"–38"
above nosings
Grip diameter
1 1/4"–2"
graspable circular
A handrail is required under IRC 2021 for a flight of 16 risers (4+ risers).
Mounting height 2' 11 7/16" is within the IRC 2021 band of 2' 10"–3' 2" above the nosings.
A graspable circular handrail is 32–51 mm (1¼″–2″) in diameter.
How handrail length is calculated
A stair handrail has two parts to its length: the sloped grip that follows the
pitch of the flight, and the end extensions the code requires at the top and
bottom. The grip section is the hypotenuse of the stair triangle, so its length is √(total rise² + total run²) — exactly the same
diagonal as the stringer.
On top of that, the IRC and ADA require the rail to keep going past the steps so there is something to hold while stepping on and off. It must run horizontally 12″ beyond the top riser, and at the bottom continue one tread depth plus 12″ past the last riser. Stairs Calc adds both extensions to the length you order — or you can switch them off to see just the sloped grip run.
Worked example
Take the canonical 16‑riser flight: a 9′‑7″ rise over a 13′‑9″ run (15 treads at 11″). The sloped grip length is √(2921² + 4185²) ≈ 5104 mm (16′‑9″). Adding the 12″ top extension and the 23″ bottom extension (one 11″ tread + 12″) brings the rail to roughly 5993 mm — about 19′‑8″ of handrail to buy.
Mounting height and grip by code
Length is only half the job — the rail also has to sit at the right height and be graspable. Stairs Calc reads the same 80‑plus‑jurisdiction handrail dataset the rest of the site checks against, so the mounting band moves with your building code:
- IRC, IBC and ADA (US) — top of the gripping surface 34″–38″ above the nosings.
- UK (Approved Document K) — 900 mm–1000 mm above the pitch line.
- Grip diameter — a graspable circular handrail is 1¼″–2″ across, so a hand can close around it.
Whether a rail is required at all also varies: the IRC asks for one at four or more risers, while the IBC, ADA and most international codes require a handrail on every flight. Pick your jurisdiction and the calculator flags the requirement, the height band and the grip range for you.
Frequently asked questions
How do I calculate handrail length for stairs?
The grip section follows the slope, so its length is the hypotenuse of the flight: √(total rise² + total run²). Then add the code end extensions. For a 2921 mm rise over a 4185 mm run that sloped length is about 16′‑9″, before extensions.
How far does a handrail have to extend past the stairs?
Under the IRC and ADA the rail extends horizontally 12″ beyond the top riser, and at the bottom it runs one tread depth plus 12″ past the last riser. Stairs Calc adds these extensions to the ordered length automatically; turn them off to see just the sloped grip run.
What height should a stair handrail be?
Most US codes (IRC, IBC, ADA) put the top of the gripping surface 34″–38″ above the nosings; the UK (Part K) allows 900 mm–1000 mm. Pick your building code and Stairs Calc checks your mounting height against that exact band.
When is a handrail required on stairs?
It depends on the code: the IRC requires a handrail at four or more risers, while the IBC, ADA and most international codes require one at every flight. The calculator flags whether your riser count needs a rail under the selected jurisdiction.
What diameter should a stair handrail be?
A graspable circular handrail is 1¼″–2″ in diameter so a hand can close around it. Non‑circular and larger profiles must meet separate graspability rules in your code.
Related stair calculators
Written by the Stairs Calc editorial team. Methodology and code references: see our methodology.
Built and maintained by builders, drafters and engineers who plan stairs for a living — every code limit is transcribed from the published standard and cited to its exact section.
Last reviewed 2026-06-20 against IRC 2021/2024
Stairs Calc gives accurate geometry and checks it against published building-code limits, but results are estimates for planning. Codes are adopted and amended locally and change over time. Always confirm dimensions against your local adopted code and a licensed professional before you build.