How do I calculate the number of stairs?

Divide the floor-to-floor rise by 7.75 in and round up. 108 in ÷ 7.75 = 13.9, so 14 risers at 7.71 in each.

What is the maximum riser height?

IRC R311.7.5.1 sets it at 7¾ in, with no more than ⅜ in difference between risers in a flight. Your local code may amend it.

What is the minimum tread depth?

IRC R311.7.5.2 sets it at 10 in, measured between the nosings of adjacent treads.

Why is there one fewer tread than risers?

The upper floor is the last step. 14 risers rise to it, and 13 treads sit between them.

HyreRemodel tools

Stair calculator

Enter the finished floor-to-floor rise and the tread depth you plan to use.

A stair calculator divides the total rise by the maximum riser height to find the number of risers. The IRC caps risers at 7¾ in and sets a 10 in minimum tread. A 108 in rise needs 14 risers of 7.71 in and 13 treads; at 10 in each, the run is 130 in.

Work out your stair

Measurements in inches. Nothing is stored or emailed.

— Risers

— Treads and run

— Against R311.7.5

What this assumed —

Geometry only. Headroom, width and handrails are not checked.

The IRC stair limits the stair calculator uses

The stair calculator uses the riser and tread limits in IRC Section R311.7.5.

Item	Limit	Section
Riser height	Not more than 7¾ in	R311.7.5.1
Tread depth	Not less than 10 in	R311.7.5.2
Variation in a flight	Largest riser or tread no more than ⅜ in over the smallest	R311.7.5.1, R311.7.5.2
Nosing	¾ in to 1¼ in where the tread is under 11 in	R311.7.5.3

As quoted in City of Boise IRC Code Handout #437, Stair Treads & Risers (02/2022). Headroom, width and handrails are also set in R311.7; the calculator does not check them. Adoption and amendments are local.

Worked example

A 9 ft floor-to-floor stair

Risers

108 in ÷ 7.75 in = 13.9, so 14 risers. 108 ÷ 14 = 7.71 in each, under the 7¾ in limit.

Run

14 risers mean 13 treads. At 10 in each, the total run is 130 in, or 10 ft 10 in, before any landing.

Risers = total rise ÷ 7.75, rounded up. Treads = risers − 1. Run = treads × tread depth.

How to measure total rise for a stair

Total rise is finished floor to finished floor. Include the flooring that will go on both levels; a thicker finish at the top changes the last riser.

Uneven risers trip people. That is why the code limits the variation to ⅜ in within a flight. See stair rise and run.

Stairs are structural work

A new or altered stair usually needs a permit. Cutting a floor opening touches joists. Have a licensed contractor or engineer and your building department confirm the design before work starts.

Removing or altering a load-bearing wall, and cutting or notching joists beyond the permitted limits, are structural changes. They need a building permit, and the building department can require an engineer to size the beam.

What the stair calculator leaves out

The stair calculator gives geometry, not a design. It does not check headroom, width, landings, guards or handrails. See handrail code requirements and permits and approvals.

For a basement or attic project, see basement finishing and attic conversion, or plan your remodel with us.

Questions this calculator answers

How do I calculate the number of stairs?: Divide the floor-to-floor rise by 7.75 in and round up. 108 in ÷ 7.75 = 13.9, so 14 risers at 7.71 in each.
What is the maximum riser height?: IRC R311.7.5.1 sets it at 7¾ in, with no more than ⅜ in difference between risers in a flight. Your local code may amend it.
What is the minimum tread depth?: IRC R311.7.5.2 sets it at 10 in, measured between the nosings of adjacent treads.
Why is there one fewer tread than risers?: The upper floor is the last step. 14 risers rise to it, and 13 treads sit between them.

Sources and methodology

Figures dated October 22, 2026. Last reviewed August 16, 2026.

City of Boise IRC Code Handout #437, Stair Treads & Risers (02/2022) (City of Boise, retrieved October 22, 2026). IRC R311.7.5 text: risers, treads, nosings.
2021 International Residential Code, Chapter 3 (International Code Council, retrieved September 5, 2026). Section R311.7, stairways. Adoption is local.

Basement finishing Where stairs get rebuilt.
Attic conversion Where a new stair is needed.
Permit checker Whether the work needs a permit.
Insulation calculator For the attic you are opening.

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