The Stair Calculator offers a web‑based solution for determining the key dimensions needed when designing a staircase. Use the diagram placed beside the calculator as a visual aid. At the page bottom you’ll also find a conversion chart that turns common fractional measurements into decimals.
Staircases appear in countless configurations, and although erecting a simple flight might look straightforward, numerous dimensions, formulas, and regulatory provisions must be taken into account. These include the length, breadth and rise of each component, as well as the placement of doors relative to the stairs; a door swing must stay entirely on the landing or floor and must not cross any step. Below you’ll find a glossary of the most frequently used stair terminology together with a selection of typical building codes. Local jurisdictions may adopt different requirements, so anyone planning a stair project should consult the regulations that apply in their area.
Run/Tread: The run, also called the tread, is the surface you step on. Its measurement runs from the outermost edge of the step – including any nosing – down to the vertical riser. Details on nosing and riser follow later. When you calculate a staircase’s total run, do not count the tread that sits on the final riser. If a nosing projects beyond the riser, its overhang must be deducted, so the total run is not merely the sum of individual tread lengths.
Building codes generally suggest that the thread has a minimum length of 10 inches (25.4 cm).
Rise/Riser: The rise denotes the vertical distance between the top of one tread and the top of the next. It differs from the physical height of the riser because the tread thickness is excluded. The count of risers, rather than treads, determines how many steps make up the staircase.
Building codes generally suggest that the maximum height of a riser be 7.75 inches (19.7 cm)
Nosing: The nosing is the portion of a tread that extends beyond the riser beneath it. Not every stair features a nosing, but when it is present its length is added to the tread measurement. Its primary role is safety, providing extra foothold space for users.
Common building codes generally suggest that the nosing has a minimum length of 0.75 inches (1.9 cm) and a maximum length of 1.25 inches (3.2 cm).
Headroom: Headroom is the height measured from the top of a tread to the ceiling above it. While building codes for headroom are primarily intended to ensure enough room for people to comfortably use the stairs, the codes typically require far more room than the average height of a person to allow for moving larger objects such as furniture.
Building codes generally suggest at least 6 ft. 8 inches (203.2 cm) of stair headroom.
Stair Width: Width is measured across the tread, from one side edge to the other, perpendicular to the run. In stair geometry the width often exceeds the run, contrary to typical rectangle dimensions. Handrails are excluded from this measurement.
Building codes generally suggest that stairs be at least 36 inches (91.44 cm) wide.
Handrails & Guards/Guardrails: A handrail is a continuous rail that follows the incline of a stair, giving occupants something to hold while moving up or down. A guard is defined as \"a building element or assembly positioned near the open edges of elevated walkways that reduces the chance of a fall from the walking surface to a lower level.\" Guards may consist of guardrails, but can also be walls, half‑walls, benches, or other constructions.
Most building codes mandate a guard on any stairway whose overall rise exceeds 30 inches (76 cm) above the ground, and the guard must be at least 34 inches (86.36 cm) tall measured from the tread tops. Handrails are required to sit between 34 and 38 inches (86.36–96.52 cm) above the treads, with a circular profile ranging from 1.25 inches (3.18 cm) to 2.675 inches (6.79 cm) in diameter.
Stringer: A stair stringer is the load‑bearing component that holds the treads and risers in place. Typically a flight contains three stringers – one on each side and a central one. While some designs hide the stringers, they become visible on stairs with open sides. Stringers can be cut to match each step’s profile, or left uncut, allowing the tread edges to be concealed.
| 16th | 8th | 4th | 2nd | Decimal |
| 1/16 | 0.0625 | |||
| 2/16 | 1/8 | 0.125 | ||
| 3/16 | 0.1875 | |||
| 4/16 | 2/8 | 1/4 | 0.25 | |
| 5/16 | 0.3125 | |||
| 6/16 | 3/8 | 0.375 | ||
| 7/16 | 0.4375 | |||
| 8/16 | 4/8 | 2/4 | 1/2 | 0.5 |
| 9/16 | 0.5625 | |||
| 10/16 | 5/8 | 0.625 | ||
| 11/16 | 0.6875 | |||
| 12/16 | 6/8 | 3/4 | 0.75 | |
| 13/16 | 0.8125 | |||
| 14/16 | 7/8 | 0.875 | ||
| 15/16 | 0.9375 | |||
| 16/16 | 8/8 | 4/4 | 2/2 | 1 |