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Stairs Calc

Stair Terminology Glossary

Every stair term used across Stairs Calc, defined in plain language — from total rise and going to throat, nosing and the walkline.

Total rise
Vertical distance from the lower finished floor to the upper finished floor.
Riser height
The vertical height of a single step; every riser must be equal within 3⁄8 in.
Run (going)
The horizontal depth of one step, measured nosing-to-nosing, not counting the overhang.
Tread
The horizontal board you step on; its depth equals the run plus the nosing.
Nosing
The lip of the tread that overhangs the riser below; ¾–1¼ in in the IRC.
Riser (board)
The vertical board that closes the gap between two treads on a closed-riser stair.
Stringer
The notched board that carries the treads and risers; usually a 2×12.
Throat
The solid wood left behind a stringer notch; keep it at least 3½ in.
Stringer length
The diagonal length of the stringer, the hypotenuse of total rise and total run.
Total run
The horizontal distance the whole flight covers, floor to floor.
Number of risers
How many equal steps the flight has; total rise divided by target riser, rounded.
Headroom
Vertical clearance measured plumb above the nosing line; minimum 6 ft 8 in (IRC).
Landing
A flat platform that breaks a flight or changes its direction.
Stringer mount (standard vs flush)
Whether the top tread sits one riser below, or level with, the upper floor.
Walkline
The path 12 in in from the inside of a turn, where winder tread depth is measured.
Winder
A wedge-shaped tread that turns a staircase without a flat landing.
L-shaped stairs
A staircase with a 90° turn, made with a quarter landing or winders.
Spiral staircase
A helical stair whose wedge treads wind around a central column.
Tread angle (rotation)
The plan-view angle each spiral or winder tread sweeps around the center.
Stair angle (pitch)
The slope of the flight in degrees; comfortable stairs sit around 30–37°.
Stair width
The clear walking width of the flight; IRC minimum 36 in above the handrail.
Handrail
The graspable rail along a stair; code height 34–38 in above the nosing line.
Guardrail (guard)
The barrier protecting an open edge; minimum 36 in high (IRC residential).
Baluster (spindle)
The vertical infill posts of a railing; gaps must reject a 4 in sphere.
Newel post
The sturdy anchor post at the end or turn of a railing.
Cable railing
A guard infilled with tensioned horizontal cables instead of balusters.
Glass railing
A guard infilled with tempered glass panels instead of balusters.
Stairwell opening
The hole framed in the upper floor that the staircase rises through.
Blondel formula (2R + T)
The comfort rule that twice the rise plus the run should equal 24–25 in.
Flight
An uninterrupted run of steps between floors or landings.
Finished floor
The walking surface after flooring is laid, from which total rise is measured.
Waist slab
The inclined structural slab beneath cast concrete stairs.
MET value
A metabolic-equivalent rate used to estimate calories burned climbing stairs.
Bullnose step
A rounded starting step, wider than the flight, that wraps past the newel.
Volute
The spiral scroll that terminates a handrail over the bullnose step.
Half-landing
A full-width landing where a stair reverses 180° in a U-shaped flight.
Stair soffit
The finished underside of a staircase or its landing.
Balustrade
The complete railing assembly: handrail, balusters, and newel posts together.
Kite winder
The central, kite-shaped winder tread at a 90° turn made of three winders.
Nosing return
The mitred end-cap that finishes an open-side tread nosing flush with the skirt.
Open-riser stair
A stair with no riser boards, leaving a gap between treads; gap rejects a 4 in sphere.
Plumb cut & seat cut
The vertical and horizontal end cuts that let a stringer meet the floors.
Handrail extension
The code-required horizontal run a handrail must extend past the top and bottom steps.
Skirt board (string board)
The trim board against the wall that the treads and risers butt into.
Ramp slope
The rise-to-run ratio of an accessible ramp; ADA caps it at 1:12.

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.