Stair Calculator

Total rise (in). Total finished rise is the vertical distance from the top of the finished lower landing to the top of the finished upper landing. Establish both finish elevations before measuring; the distance between bare subfloors can be different. This full height is divided into equal finished risers.

Maximum target riser (in). Enter the greatest riser height you intend to use for this stair. The calculator rounds the number of risers upward, then divides the full rise equally among them. This is your selected limit, not a determination of the permitted height for your project.

Tread depth / going (in). Unit run, also called going, is the horizontal advance from one step to the next. Use the horizontal distance between successive riser planes, or between corresponding nosings. Do not add the tread’s nosing projection to this value; the physical tread board may be deeper than the unit run.

Tread thickness (in). Measure the actual vertical thickness of the tread assembly above each horizontal stringer seat. Include a finish layer if it is part of the assembly that raises the walking surface above that seat. Leave this field blank for geometry alone. The bottom-cut result assumes the stringer bears directly on the finished lower landing; it is not the right deduction when the stringer sits below that finish elevation.

Finished riser height is the vertical distance between successive walking surfaces; every finished rise stays equal. The framing-square setting uses that full rise and the entered unit run. When tread thickness is entered, the bottom adjustment is one tread thickness and the bottom rise cut is the finished rise minus that thickness. This shorter bottom cut compensates for the tread placed above its seat; do not use it as the square’s repeated rise setting. The upper landing replaces the last tread, so there is one fewer separate tread than risers. Total run is the horizontal projection of those treads. The flight diagonal is only a geometric reference, not the stringer’s stock length or an exact end-to-end cutting dimension.

Risers = round up(total rise ÷ maximum target riser).
Uniform riser = total rise ÷ risers.
Treads = risers − 1.
Run (in) = treads × tread depth.
Approximate diagonal (ft) = √(rise² + run²) ÷ 12.
Conventional bottom rise cut = finished riser height − actual tread thickness.

Worked example: A 108 in finished rise and 7.5 in target produce 15 equal risers at 7.2 in, with 14 treads at 10 in for 140 in total run. The 7 3/16 in display reference is approximate; repeating it would change the total rise. The overall diagonal is approximately 14.7347 ft and is not a cut-ready stringer.

Geometry aid only, not code-compliance or structural stair design. The diagonal is not a cut-ready stringer length. Stringer stock, cuts, attachments, landing details, guards, and handrails need separate design.

For example, a 7 1/2 in finished rise with a 1 in tread has a 6 1/2 in bottom rise cut. The repeated square setting remains 7 1/2 in rise, not 6 1/2 in. If the lower finish is not in place, the stringer bears on a different surface, or the attachment details differ, establish those elevations and connections before cutting. No top-cut dimension is supplied because tread thickness alone does not establish the top attachment.

Layout references: Decks.com stringer layout and Fine Homebuilding: basic stair stringers. Check the project’s actual details rather than adopting a reference example as a specification.