Stair Stringer Calculator

Turn total rise into the number of risers, riser height, tread run, stringer length and stair angle, checked against IRC riser and tread limits.

Measure vertically from the finished lower surface to the finished upper floor or deck surface.
The 2021 IRC allows at most 7¾ in (196 mm). A lower target such as 7 in gives a gentler stair.
Horizontal distance between the leading edges of adjacent treads. The IRC minimum is 10 in (254 mm).
Number of risers
14 risers
Riser height
7.714
Number of treads
13 treads
Total run
130.00
Stringer length (along the slope)
14.08
Rise-to-run hypotenuse; buy a longer board to allow for the top and bottom cuts.
Stair angle
37.6
Code check
Within IRC R311.7.5 riser (≤ 7¾ in) and tread (≥ 10 in) limits and the 151 in flight limit. Local codes may differ.

Estimate generated with SortedSums: https://sortedsums.com/stair-stringer-calculator/. For informational purposes only; verify before relying on it.

Estimate only. This tool is for informational and educational purposes. Results depend on your inputs and simplifying assumptions, and are not a substitute for professional engineering, design or financial advice. Always verify with a qualified professional and applicable codes before purchasing, building or making decisions.

How it’s calculated

Divide the total rise by the largest riser you will allow and round up to get the number of risers. Every riser is then the same height. With the upper floor acting as the last step there is one tread fewer than risers.

Risers = ⌈ total rise ÷ max riser ⌉ Riser height = total rise ÷ risers Treads = risers − 1 Total run = treads × tread run Stringer length = √(total rise² + total run²) Angle = atan(riser ÷ tread)

Example: a 108 in rise with a 7¾ in maximum: 108 ÷ 7.75 = 13.94, so 14 risers of 108 ÷ 14 = 7.714 in. 13 treads × 10 in = 130 in of run. Stringer = √(108² + 130²) = 169.0 in = 14.08 ft. Angle = atan(7.714 ÷ 10) = 37.6°.

2021 IRC limitValue
Maximum riser height (R311.7.5.1)7¾ in (196 mm)
Minimum tread depth (R311.7.5.2)10 in (254 mm)
Maximum rise of one flight (R311.7.3)151 in (3835 mm)

The IRC also limits how much risers and treads may vary within a flight and sets headroom, width, nosing and handrail rules. Check the code your jurisdiction has adopted.

Frequently asked questions

How many steps do I need for a 9 foot rise?

A 108 in rise needs 14 risers of about 7.71 in at the IRC maximum of 7¾ in, with 13 treads.

What is the maximum stair riser height?

The 2021 International Residential Code allows a riser of at most 7¾ in (196 mm) and requires a tread depth of at least 10 in (254 mm). Commercial (IBC) stairs are stricter.

How long should my stair stringer board be?

At least the calculated stringer length plus allowance for the plumb and level cuts. For a 14 ft stringer most builders buy a 16 ft board.

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Sources

Formulas are taken from the free public references above. Results are provided “as is” for informational and educational purposes only. See our disclaimer.

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