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Stair Calculator
Calculate risers, treads, stair angle, and stringer length from total rise. Includes IRC R311.7 code check and materials list.
Stair dimensions
Finished floor to finished floor
Nosing to nosing
IRC max 7.75 in
IRC 34-38 in
Risers and treads
14 risers, 13 treads
- Riser height
- 7.71 in
- Tread depth
- 10.75 in
- Total run
- 130 in
- Stair angle
- 37.65 deg
- Slope
- 0.77 rise/run
- Stringer length
- 169.01 in
- 2R + T
- 25.43 in
- IRC compliant
- Yes
Materials list
- Stringers
- 3
- Treads
- 13
- Risers
- 14
Code and comfort notes
- 2R + T = 25.43 in falls outside the 24-25 in stair-builder rule.
Frequently Asked Questions about the Stair Calculator
How many stairs do I need for my total rise?
Divide your total floor-to-floor rise by the maximum allowed riser height, then round up. The IRC caps residential risers at 7.75 in, so a 108 in (9 ft) rise needs ceil(108 / 7.75) = 14 risers. Actual riser height equals total rise divided by that count.
What is the difference between rise, run, and tread depth?
Rise is the vertical jump between steps; run is the horizontal distance between nosings. Tread depth is the actual board width, equal to run plus nosing projection minus the part overlapped by the riser below.
What does the IRC require for residential stairs?
IRC R311.7 caps risers at 7.75 in (R311.7.5.1) and requires tread depth at least 10 in (R311.7.5.2). Handrail height is 34-38 in above the nosing line (R311.7.8.1). The calculator flags any value that breaks these limits.
What is the 2R + T stair-builder rule?
Carpenters target 2 times the riser plus the tread run between 24 and 25 in. Shorter risers pair with deeper treads; taller risers with shallower ones. The IRC does not require this; the calculator shows it as advice.
How long does my stringer need to be?
Stringer length is the hypotenuse of total rise and total run. For a 108 in rise with 13 treads at 10 in (130 in run), the stringer is sqrt(108^2 + 130^2) = 169.01 in. Stairs over 120 in stringer usually need a third center stringer.