Staircase Calculator
Size a staircase from total rise to finished cost with this free stair calculator: riser & tread solver, straight-run and headroom planner, L-shape & U-shape layouts, stringer cut lists, an IRC code checker, material takeoff, and a DIY-vs-pro cost estimator. All math runs in your browser — nothing is uploaded.
Scope: this tool sizes the stairs themselves (steps, stringers, landings, code). For carpet yardage computed from stair dimensions, see our carpet calculator.
Riser & Tread Solver
This stair riser calculator picks the riser count that lands closest to your ideal riser height, then enforces the IRC 7.75-in maximum; the stair tread calculator half of the solver checks tread depth against the 10-in IRC minimum. Enter floor-to-floor rise to start.
Straight-Run & Headroom Planner
This rise and run stair calculator doubles as a stair headroom calculator: enter floor-to-floor rise and tread depth to get total run, stringer length, the stair angle calculator reading (pitch in degrees), and the stairwell opening you need for 80-in headroom along the whole run.
L-Shape & U-Shape Planner
This l shaped stair calculator and u shaped stair calculator split the total rise across two runs with a code-size landing — a stair landing calculator for 90° and 180° turns. Landing depth defaults to the stair width (min 36 in per IRC R311.7.6).
Stringer Layout
This stair stringer calculator gives you a cut list per step, throat-depth safety check, stringer count by width, and the 2×12 boards to buy. The built-in stair stringer length calculator treats each stringer as the hypotenuse of total rise and total run.
Stair Code Calculator IRC baseline — check local code
This irc stair code checker checks your numbers against IRC R311.7 / R312.1 — including the stair riser height code 7.75 in maximum and the stair tread depth code 10 inch minimum. Local amendments always win — this is a planning aid, not an inspection certificate.
Material Takeoff
This stair material calculator builds a shopping list from your stair numbers. Board counts assume standard 12-ft tread/riser stock and one board per stringer; add your waste below or in the cost tab.
Baluster spacing (the 4-in sphere rule on stairs) is a layout of its own — see our baluster calculator for exact spacing.
Stair Cost Estimator
DIY lumber vs. pro install. Prices are rough 2026 US averages — edit every price to your local store before buying.
Worked example: a 108-in (9-ft) floor-to-floor stair
Every number on this page comes from one consistent calculation — change the inputs above and all seven modes update together.
| Quantity | Value | How |
|---|---|---|
| Risers | 15 at 7.2 in each | round(108 ÷ 7) = 15; 108 ÷ 15 = 7.2 ≤ 7.75 max |
| Treads | 14 at 11 in deep | risers − 1 (top tread is the upper floor) |
| Total run | 154 in (12 ft 10 in) | 14 × 11 |
| Stringer length | 188.1 in (15 ft 8.1 in) | √(108² + 154²) |
| Stair angle | 35.04° | atan(108 ÷ 154) |
| Comfort check | 25.4 in — comfortable | 2R + T = 2×7.2 + 11 (ideal 24–25) |
| Stringers for 36-in width | 3 cut stringers | ≤ 18 in on center: ⌈36 ÷ 18⌉ + 1 |
| Throat depth | 5.36 in — OK | 11.25 − 7.2·cos(35.04°) ≥ 3.5 in min |
| Stairwell opening | 131.19 in (10 ft 11.2 in) | keeps 80-in headroom with 12-in floor assembly |
| L-shape split (8 + 7 risers) | 113 × 102 in footprint | 77-in lower run + 66-in upper run + 36×36 landing |
| U-shape split (8 + 7 risers) | 113 × 72 in footprint | 77-in runs side by side + 36×36 landing |
| Takeoff | 3× 2×12×16 ft, 4× 2×12×12 ft, 4× 1×8×12 ft, 28 balusters | 4 treads per 12-ft board; 2 balusters per tread |
| Cost | $621.50 DIY · $2421.50 pro installed | materials + 10% waste; pro adds $1,800 labor |
Staircase questions, answered
How many steps do I need for stairs, with a 9-foot (108 in) floor-to-floor rise?
15 risers at 7.2 in each (108 ÷ 15). That gives 14 treads at 11 in deep and a total run of 154 in (12 ft 10 in). The stringer works out to 188.1 in (15 ft 8.1 in) at a 35.04° pitch — comfortably under the 7.75-in IRC riser maximum.
What is the 7–11 rule for stairs?
A 7-in riser paired with an 11-in tread — the classic 7-11 rule stairs combination. It satisfies the stair comfort formula 2R + T = 25 (2×7 + 11), inside the ideal 24–25 in band, and meets IRC limits (riser ≤ 7.75 in, tread ≥ 10 in).
What is the maximum riser height allowed by code?
7.75 in under IRC R311.7.5.1, and the tallest and shortest risers in one flight must not differ by more than 3/8 in. The 108-in example on this page uses 7.2-in risers — under the max with room to spare. Always check local code; some jurisdictions amend the IRC.
How long should stair stringers be?
This stair stringer length calculator treats the stringer as the hypotenuse of the total rise and total run: √(108² + 154²) = 188.1 in (15 ft 8.1 in) for the example stair. Buy 2×12 boards at the next standard length up — 16 ft here — and add mid-span support on stringers longer than 10 ft.
How many stringers do I need?
The short answer to "36 inch wide stairs how many stringers" is three: cut stringers must be spaced no more than 18 in on center, so ⌈36 ÷ 18⌉ + 1 = 3 stringers. Anything wider than 36 in needs at least four.
How much headroom do stairs need, and how big must the stairwell opening be?
IRC requires 80 in (6 ft 8 in) of headroom along the whole run (R311.7.2). For the 108-in example with a 12-in floor assembly, the upper floor must open within 22.81 in of the stair base — a stairwell opening at least 131.19 in (10 ft 11.2 in) long.
When is a handrail required on stairs?
On at least one side of any flight with 4 or more risers (IRC R311.7.8) — so the 15-riser example on this page needs one. Rail height must be 34–38 in measured vertically above the tread nosings.
What size landing do L-shaped and U-shaped stairs need?
This stair landing calculator covers both turns: at least 36 in measured in the direction of travel and no narrower than the stair itself (IRC R311.7.6) — use 36×36 in for a 36-in stair. Splitting the 108-in example into 8 + 7 risers gives a 77-in lower run and a 66-in upper run: the L footprint is 113 × 102 in, the U footprint 113 × 72 in.
Are open risers allowed?
Yes, if the gap between treads will not pass a 4-in diameter sphere (IRC). Stair nosing requirements IRC R311.7.5.3: with solid risers and treads under 11 in deep, nosings of 3/4 to 1-1/4 in are required; with open risers there is no nosing requirement.
Can I use this as a deck stair stringer calculator?
Yes — deck stairs use the same rise/run math. Enter your deck's floor-to-deck-board rise and this deck stair stringer calculator returns riser count, stringer length, and the 2×12 cut list. Outdoors, build from pressure-treated 2×12 and confirm guard, handrail, and footing rules with local code.
Does this work as a basement stairs calculator?
Yes. Measure from the basement slab to the finished floor above and enter it as total rise; this basement stairs calculator then sizes risers, treads, and stringers like any other flight, and the headroom planner sizes the stairwell opening for the 80-in IRC minimum — the part most basement remodels get wrong.