Calculator
Stair and step layout helper
Enter the total rise and the riser height or count you want, plus the tread depth. You get the number of risers and treads, the exact riser height, the run, the stringer length and angle, and a drawing of the stringer.
Your stair
JavaScript is off, so this page cannot do the math for you. Use the formulas below: divide the total rise by your target riser height and round up to get the number of risers, then divide the total rise by that number.
If you fill in the number of risers, it replaces the target height.
Run per step, measured level from the front edge of one tread to the front edge of the next. Nosing overhang is added separately below.
Risers —
Treads —
Riser height —
Tread run —
Tread board depth with nosing —
Total run —
Stringer length (approximate, along the nosing line) —
Stair angle —
Hypotenuse of total rise and total run, before end cuts and the bottom-riser adjustment for tread thickness. Buy longer stock.
Comfort checks (rules of thumb)
- —
- —
2021 IRC R311.7 residential limits
- — Riser height not more than 7-3/4″
- — Tread depth not less than 10″
- — Nosing 3/4″ to 1-1/4″ (not required where tread depth is at least 11″)
- — Flight rise not more than 151″ between floors or landings
- Within a flight, the tallest riser can be no more than 3/8″ taller than the shortest, and the deepest tread no more than 3/8″ deeper than the shallowest (risers measured vertically between tread front edges, treads measured level nosing to nosing). Nosings can vary by no more than 3/8″ within a stairway. This layout makes them all equal, so keep your cuts and finished floor heights consistent.
- Headroom at least 6 ft 8 in, measured up from the sloped line of the nosings. Check this on site; the helper cannot.
Enter a total rise, a target riser height or number of risers, and a tread run above zero.
Stringer layout
Simple side view, drawn to scale from your numbers. The dashed line is the nosing line.
The math
Risers = total rise ÷ target riser height, rounded up (or the count you enter). Riser height = total rise ÷ risers. Treads = risers − 1, because the upper floor is the last step. Total run = treads × tread run. Stringer length = √(total run² + total rise²). Angle = arctan(riser ÷ tread run).
Worked example
Total rise 105″, target riser 7-1/2″: 105 ÷ 7.5 = 14 risers of exactly 7-1/2″, so 13 treads. At a 10″ run the total run is 13 × 10 = 130″. Stringer length = √(130² + 105²) = √27,925 ≈ 167-1/8″. Angle = arctan(7.5 ÷ 10) ≈ 36.9°. Comfort: 2 × 7.5 + 10 = 25″ and 7.5 + 10 = 17.5″, both in range. Riser 7-1/2″ is under 7-3/4″ and tread 10″ meets the 10″ minimum; with a 10″ tread the IRC needs a 3/4″ to 1-1/4″ nosing.
About the comfort checks
The 2R+T rule is usually credited to the French architect François Blondel (1675); the R+T rule is a common carpentry guideline. They are rules of thumb, not code requirements, and we did not find an authoritative standard for the exact ranges. Use them to compare options; the code limits are the ones that must be met.
Sources
Code limits are from the 2021 International Residential Code, Section R311.7 (Stairways), as published by the ICC, checked October 25, 2026. Your jurisdiction may use a different edition or local amendments.
This tool gives layout estimates for planning only. It is not engineering, professional or code advice and is not a code approval. It does not size stringers or check loads, spans, guards, handrails, width, headroom on site, or fastening. Your local building code and building official decide what's required, and you are responsible for the design, construction and safety of your own build.
This calculator runs in your browser only. Your numbers aren't sent to us or anyone else, and the calculator doesn't save them. The page itself uses analytics; see our privacy policy.
Related on this site
We pick tools from independent tests and reviews, not our own testing.