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Stair Calculator: Risers, Treads, Run and Stringer Length

Work out the number of steps, riser height, tread depth and stringer length for a straight staircase from its total rise and run. Enter the height floor to floor, the riser and tread you aim for, and see the exact layout, the stair angle and how it measures up to the IRC limits.

Your numbers

ft
in

Finished floor to finished floor (or deck surface to the ground or landing).

in

The step height you aim for. The stair uses the next whole number of risers, so each one comes out at or under this.

in

Nosing to nosing, measured level.

in

How far the tread sticks out past the riser below.

in

Actual thickness: 5/4 decking is about 1 in, 2x lumber 1-1/2 in.

For the throat: the wood left under the notches.

in

In inches, if the stair has to fit a set length (120 in = 10 ft).

Steps

–

Riser height
–
Tread depth
–
Total run
–
Stair angle
–
2 risers + 1 tread
–
Stringer length (slope)
–

Code check (IRC R311.7)

Enter the total rise to check the stair.

Headroom: the IRC asks for at least 6 ft 8 in, measured straight up from the line along the nosings.

An estimate for layout and pricing. Codes vary by place: the local code and your inspector have the final word.

The calculation runs in your browser and ParrotNotes does not store your numbers. They sit in the page address so you can bookmark or share the result.

How to calculate stairs

Start with the total rise: the height from the finished floor at the bottom to the finished floor at the top. Divide it by the riser height you want and round up to get the number of risers, then divide the rise by that whole number to get the exact riser height. There is one tread fewer than there are risers, because the top floor is the last step.

Worked example: a rise of 8 ft 7 in is 103 in. At a target of 7-1/2 in, 103 ÷ 7.5 = 13.7, so the stair has 14 risers of 103 ÷ 14 = 7.36 in (7-3/8 in) and 13 treads. With 10 in treads the total run is 13 × 10 = 130 in, or 10 ft 10 in, and the stair climbs at about 36 degrees.

Stair code: the IRC limits for houses

The International Residential Code, section R311.7, sets the numbers most US jurisdictions start from. A riser may be at most 7-3/4 in and a tread at least 10 in, measured nosing to nosing. In one flight the tallest riser may not beat the shortest by more than 3/8 in, and the same goes for treads, which is why the calculator divides the rise evenly.

Treads under 11 in need a nosing of 3/4 to 1-1/4 in. Headroom is at least 6 ft 8 in, measured straight up from the line along the nosings, a flight may rise no more than 12 ft 7 in before a landing, and the stair is at least 36 in wide. Handrails sit 34 to 38 in above the nosings. States and cities adopt the IRC with their own changes, so the local code and the inspector decide.

The comfort rule: 2 risers + 1 tread = 24 to 25 in

Code limits keep a stair safe; the comfort rule keeps it pleasant. A common rule of thumb says two risers plus one tread should add up to 24 to 25 in, close to a natural stride. The 103 in example gives 2 × 7.36 + 10 = 24.7 in, inside the range.

A steep stair (7-3/4 in risers, 10 in treads) comes to 25.5 in and feels short-stepped; 6 in risers with 12 in treads come to 24 in and feel easy but take a lot more floor. If the run has to fit a set space, enter it and the calculator says whether the layout fits and which tread depth would fill it.

Cutting the stringers

A cut stringer covers the slope from the bottom to the top, the square root of rise squared plus run squared: about 165.9 in (13 ft 10 in) for the example, so a 14 ft board. Lay out the notches with the exact riser and tread, then cut the bottom riser shorter by the tread thickness, so the first step comes out the same height as the rest once the treads are on.

The wood left under the notches is the throat. On a 2x12 (11-1/4 in actual) with 7-3/8 in risers and 10 in treads, about 5.3 in remains; on a 2x10 (9-1/4 in) only about 3.3 in. Check the stringer size, spacing and span against your local code or a prescriptive deck guide before you cut.

On the site visit

Measure the rise at the stair's location, from finished floor to finished floor. If the bottom floor or the deck surface is not finished yet, add the flooring or decking thickness, or the first or last step will come out different from the rest.

Then write down what the customer wants that the numbers do not show: tread and riser material, open or closed risers, the railing style, whether there is a landing, and who pulls the permit. Those details move the price as much as the step count does.

Sources, checked October 2026. All figures are estimates; the local code decides:

More for contractors and building-materials sales: Building materials sales, Construction daily report, Construction meeting minutes template.

The tape measure gives you the rise. The customer gives you the rest.

The numbers come from the site visit, and so does everything else the quote needs: the tread material they picked, the railing, who pulls the permit, when they want it done. Record the walk-through in ParrotNotes and get the summary and next steps, so the quote matches what the customer asked for.

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