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Stair Stringer Calculator

Lay out perfect stairs from total rise: riser height, tread depth, step count, stringer length and stair angle.

Stair layout

Measure total rise first. Results update live.

Riser height
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Enter the total rise to lay out the stairs.

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Why risers must be equal

Building codes require every riser in a flight to be the same height within a small tolerance, because even a quarter inch difference is a trip hazard. The calculator divides the total rise into equal risers by rounding the step count up, then recalculates the exact riser height.

Riser plus tread comfort rule

A comfortable stair keeps riser height plus tread depth near 17 to 18 inches. With a 7.5 inch riser and 10 inch tread you get 17.5, which feels natural to climb and meets most residential codes.

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Stair Stringer Calc FAQs

What is the maximum riser height allowed?
Most residential codes cap risers at 7.75 inches and require treads at least 10 inches deep. Always confirm with your local building department before cutting stringers.
How long a board do I need for the stringer?
The calculator shows the stringer length and the smallest standard board that fits it, usually a 2 by 12. Buy one size longer if you are unsure.
Why is the total run based on steps minus one?
The top step is the deck or landing surface itself, so a flight of 14 risers needs 13 treads. The stringer run is therefore tread depth times steps minus one.
Can I use this for deck stairs?
Yes, it is ideal for deck stairs. Measure total rise from the ground or footing top to the deck surface, and use pressure treated 2 by 12 lumber for the stringers.
What stair angle is comfortable?
Residential stairs usually land between 30 and 37 degrees. Steeper than 40 degrees feels ladder like and may fail code for primary stairs.
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