Stair Calculator

Enter the total vertical rise from floor to floor and your preferred tread depth. You get the number of steps, the exact riser height, the total run and the length of the stringer board.

Results

Number of risers

15 risers

Each 7.200 in tall

Riser height: 7.200 in
Number of treadsThe upper floor acts as the top tread: 14 treads
Total run: 140.0 in
Total run: 11.67 ft

Stringer

Stringer length (hypotenuse): 14.73 ft
Board to buy (standard length): 16 ft
Angle of stairs: 37.6 degrees

Check against typical US code (IRC)

Riser ≤ 7¾ in: Yes
Tread ≥ 10 in: Yes
Comfort check 2 × riser + tread (ideal 24–25 in): 24.4 in

Every riser must be the same height (within 3/8 in). Local codes differ and stairs are a safety item, so confirm requirements with your building department.

How this calculator works

We divide the total rise by your preferred riser height and round to a whole number of risers, then divide the total rise by that number to get the exact riser height (every step must be identical). There is always one fewer tread than risers, because the upper floor is the top step. The total run is the number of treads times the tread depth, and the stringer is the diagonal of the rise and run triangle.

risers = round(total rise ÷ target) riser = total rise ÷ risers run = (risers − 1) × tread

Worked example: a 108 in rise at a 7.25 in target gives 15 risers of 7.2 in. With 14 treads of 10 in the run is 140 in (11.7 ft), and the stringer is 14.7 ft, so buy a 16 ft board.

Tips before you buy

Riser and tread dimensions must be consistent. People trip on the odd one out, even a difference of half an inch.
Remember to account for the thickness of the finished floor and the tread boards when you measure the rise and cut the stringer.
In the US, the IRC generally limits riser height to 7¾ in, requires a minimum 10 in tread, and calls for a handrail on stairs with four or more risers. Many places have different rules, so check locally.
Cut one stringer, test it in place, then use it as the template for the others.

Tools & materials for this project

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Stair gauges Framing square Pressure-treated 2x12 Stair tread boards Circular saw

Frequently asked questions

How do you calculate stair stringers?

Divide the total rise by a target riser height, round to a whole number to get the number of risers, then divide the rise by that number for the exact riser height. Treads are one fewer than risers.

What is the ideal riser height?

Between 7 and 7¾ inches. Most codes cap it at 7¾, and 2 × riser + tread should come to about 24 to 25 in for a comfortable stair.

How long a board do I need for a stringer?

It has to cover the diagonal from top to bottom, plus a little margin. A 9 ft rise needs about a 16 ft board, which is why many stringers are 2×12 in 16 ft lengths.

Related calculators & guides

Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.

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