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Design a safe, comfortable staircase from a single measurement. Enter your total rise and this calculator works out the number of steps, exact riser height, tread depth, total run, stair angle, and stringer length — then checks every dimension against IRC or IBC building code as you type.
Everything updates live, including the drawing and code checks.
Design estimate from your inputs. Always confirm against your local building code before you cut.
To calculate stairs, divide the total rise (floor-to-floor height) by your target riser height and round to a whole number — that is your number of risers. Then divide the total rise by that number for the exact riser height. Treads equal risers minus one, and total run = treads × tread depth. Stringer length = √(rise² + run²). A 108 in rise needs 14 risers at 7.71 in with a 136.5 in run.
Five steps. The elevation drawing, dimensions, and code checks all update as you type.
Straight, L-shaped, U-shaped, spiral, deck, concrete, floating, or custom. Each type sets sensible starting dimensions you can still edit.
Measure from the finished lower floor to the finished upper floor — not floor to ceiling. This single number drives the whole design.
Enter the riser height you want and the tread depth. The calculator rounds to a whole number of risers and gives you the exact riser height to build.
Select IRC for residential or IBC for commercial. Every dimension is checked live against the limits, with pass, warning, or fail flags.
Get the run, angle, stringer length, material list, and cost. Then print the stringer cut template, copy, share, export CSV, or save the design to compare.
Stair design starts from one fixed number — the total rise — and works outward. Every step of that logic is shown here with worked figures.
Why treads = risers − 1: the last riser brings you up to the finished floor, which acts as the final tread. Forgetting this is the most common stair-layout mistake and leaves you one tread short.
Example — a 108 in (9 ft) floor-to-floor rise with a 7.5 in target riser: 108 ÷ 7.5 = 14.4, which rounds to 14 risers. Exact riser height = 108 ÷ 14 = 7.71 in. Treads = 13, so with a 10.5 in tread the total run is 136.5 in. The angle is arctan(7.71 ÷ 10.5) = 36.3°, and the stringer is √(108² + 136.5²) = 174.1 in.
Common staircases in imperial and metric, calculated with the same formulas as the tool above.
| # | Project | Total rise | Risers | Riser height | Tread | Total run | Angle |
|---|---|---|---|---|---|---|---|
| 1 | Residential indoor stair | 108 in | 14 | 7.71 in | 10.5 in | 136.5 in | 36.3° |
| 2 | Basement stair | 96 in | 13 | 7.38 in | 10 in | 120.0 in | 36.4° |
| 3 | Second-floor stair | 117 in | 16 | 7.31 in | 10.5 in | 157.5 in | 34.9° |
| 4 | Garage step-up | 21 in | 3 | 7.00 in | 11 in | 22.0 in | 32.5° |
| 5 | Deck stair (low) | 36 in | 5 | 7.20 in | 11 in | 44.0 in | 33.2° |
| 6 | Deck stair (standard) | 48 in | 6 | 8.00 in | 11 in | 55.0 in | 36.0° |
| 7 | Deck stair (tall) | 72 in | 10 | 7.20 in | 11 in | 99.0 in | 33.2° |
| 8 | Porch steps | 24 in | 4 | 6.00 in | 12 in | 36.0 in | 26.6° |
| 9 | Outdoor concrete steps | 42 in | 6 | 7.00 in | 12 in | 60.0 in | 30.3° |
| 10 | Loft stair (steep) | 84 in | 10 | 8.40 in | 9 in | 81.0 in | 43.0° |
| 11 | Tiny-house stair | 90 in | 11 | 8.18 in | 9 in | 90.0 in | 42.3° |
| 12 | Attic stair | 99 in | 12 | 8.25 in | 9.5 in | 104.5 in | 41.0° |
| 13 | Office stair (IBC) | 144 in | 21 | 6.86 in | 11 in | 220.0 in | 31.9° |
| 14 | Commercial stair (IBC) | 132 in | 19 | 6.95 in | 11 in | 198.0 in | 32.3° |
| 15 | School stair (IBC) | 156 in | 23 | 6.78 in | 11.5 in | 253.0 in | 30.5° |
| 16 | Steel access stair | 120 in | 17 | 7.06 in | 11 in | 176.0 in | 32.7° |
| 17 | Floating stair | 110 in | 16 | 6.88 in | 11 in | 165.0 in | 32.0° |
| 18 | Split-level stair | 60 in | 8 | 7.50 in | 10.5 in | 73.5 in | 35.5° |
| 19 | Sunken living room | 14 in | 2 | 7.00 in | 11 in | 11.0 in | 32.5° |
| 20 | Pool deck stair | 30 in | 4 | 7.50 in | 11 in | 33.0 in | 34.3° |
| 21 | House stair (metric) | 2,700 mm | 15 | 180 mm | 280 mm | 3,920 mm | 32.7° |
| 22 | Apartment stair | 2,600 mm | 15 | 173 mm | 270 mm | 3,780 mm | 32.7° |
| 23 | Villa stair | 3,000 mm | 18 | 167 mm | 290 mm | 4,930 mm | 29.9° |
| 24 | Basement (metric) | 2,400 mm | 13 | 185 mm | 260 mm | 3,120 mm | 35.4° |
| 25 | Duplex stair | 2,850 mm | 16 | 178 mm | 280 mm | 4,200 mm | 32.5° |
| 26 | Garden steps | 900 mm | 6 | 150 mm | 320 mm | 1,600 mm | 25.1° |
| 27 | Terrace steps | 1,200 mm | 8 | 150 mm | 300 mm | 2,100 mm | 26.6° |
| 28 | Office stair (metric) | 3,300 mm | 20 | 165 mm | 300 mm | 5,700 mm | 28.8° |
| 29 | Loft stair (metric) | 2,500 mm | 13 | 192 mm | 240 mm | 2,880 mm | 38.7° |
| 30 | Warehouse stair | 3,600 mm | 20 | 180 mm | 270 mm | 5,130 mm | 33.7° |
Riser height is the exact value after rounding to a whole number of risers. Total run assumes a single straight flight; L- and U-shaped stairs add a landing.
What the numbers mean before you order material or start cutting.
Every riser must be the same height within 3/8 in (9.5 mm). Uneven risers are the leading cause of stair falls, because people step to the rhythm the first tread sets.
Between 30° and 37° feels comfortable for everyday use. Steeper than 42° becomes a ladder-like climb and usually fails residential code.
The horizontal floor length the stair consumes. If the run does not fit, switch to an L- or U-shaped layout with a landing rather than steepening the stair.
The diagonal distance. Add roughly 12 in (300 mm) for the top and bottom cuts, and remember the bottom riser is cut down by the tread thickness.
Both drawings redraw live from your dimensions. The cut template prints cleanly for the workshop.
The sawtooth layout to mark on your stringer board, with the framing-square settings.
An axonometric view of the finished flight at your width and step count.
These update live. The first shows what happens if you add or remove a riser; the second checks your design against the comfort and code envelope.
Riser height and total run for nearby riser counts. Your current design is highlighted.
Your riser and tread combination plotted against the safe zone.
The dimensional limits most often checked by inspectors. IRC governs most one- and two-family homes in the US; IBC covers commercial and multi-family buildings.
| Requirement | IRC (residential) | IBC (commercial) | Notes |
|---|---|---|---|
| Maximum riser height | 7.75 in (197 mm) | 7 in (178 mm) | Measured vertically between tread nosings |
| Minimum tread depth | 10 in (254 mm) | 11 in (279 mm) | Nosing to nosing, excluding overhang |
| Minimum headroom | 6 ft 8 in (2032 mm) | 6 ft 8 in (2032 mm) | Vertical, from the nosing line |
| Minimum stair width | 36 in (914 mm) | 44 in (1118 mm) | IBC narrows to 36 in for low occupant loads |
| Riser / tread variation | 3/8 in (9.5 mm) | 3/8 in (9.5 mm) | Largest minus smallest within a flight |
| Nosing projection | 0.75–1.25 in | 0.75–1.25 in | Required where treads are under 11 in |
| Handrail height | 34–38 in | 34–38 in | Above the nosing line |
| Guard height | 36 in (914 mm) | 42 in (1067 mm) | Where the drop exceeds 30 in |
| Max rise between landings | 151 in (12 ft 7 in) | 144 in (12 ft) | A landing is required beyond this |
| Spiral: min tread depth | 6.75 in at 12 in | — | Measured 12 in from the narrow edge |
| Spiral: max riser | 9.5 in (241 mm) | — | Minimum headroom 6 ft 6 in |
Figures reflect widely adopted recent editions of the IRC and IBC. Local amendments are common and always take precedence — confirm with your building department before construction.
A stair calculator turns one measurement — the total rise from finished floor to finished floor — into a complete, buildable staircase layout. It works out how many risers you need, how tall each one must be, how many treads that gives you, how much floor length the stair will consume, what angle it sits at, and how long the stringers need to be. Doing this by hand is possible but easy to get wrong, and stair dimensions are unforgiving: an error of a few millimetres repeated across fourteen steps becomes a trip hazard and a failed inspection.
The reason the calculation starts with the rise is that the rise is fixed. The floor above is where it is, and every riser in the flight must be equal, so the total rise has to divide evenly into a whole number of risers. Everything else — tread depth, run, angle — follows from that division and from the space you have available.
Stairs are among the most heavily regulated elements of a building, because they cause a large share of home injuries. In the United States, the International Residential Code (IRC) governs most one- and two-family homes, and the International Building Code (IBC) covers commercial and multi-family construction. The two differ in ways that matter: the IRC permits a maximum riser of 7.75 in with a minimum tread of 10 in, while the IBC tightens this to a 7 in riser and an 11 in tread, producing a shallower, more gradual stair suited to public buildings.
Both codes require a minimum headroom of 6 ft 8 in measured vertically from the nosing line, limit the variation between the tallest and shortest riser in a flight to 3/8 in, and require a landing where the vertical rise between floors exceeds roughly 12 ft. Other jurisdictions have their own rules — the UK's Approved Document K, the Eurocodes, and Australian and Canadian standards all set comparable but not identical limits. Local amendments are common everywhere, so treat any calculator output as a design starting point and confirm it with your building department.
The riser is the vertical face between treads. Comfortable riser heights for everyday residential use fall between about 6.5 and 7.75 in (165–197 mm), with roughly 7 to 7.5 in being the sweet spot most people find natural. Lower risers feel gentle but require more treads and therefore more floor space; higher risers save space but tire people faster and are more dangerous going down. Because all risers must be equal, the calculator divides your total rise by a whole number of steps and gives you the exact value to build — which will rarely be the round number you started with.
One subtlety catches many builders: finished flooring. If you calculate from the subfloor but then add 3/4 in of hardwood at the top and tile at the bottom, your first and last risers will no longer match the rest. Always calculate from finished floor to finished floor, or account for the flooring thickness explicitly.
The tread depth, also called the going, is the horizontal distance you actually step on, measured nosing to nosing. Deeper treads are safer, particularly on the way down, because more of the foot lands on the step. Residential minimums start at 10 in under the IRC, but 11 in is noticeably more comfortable and is the IBC requirement. Deep treads combined with tall risers, or shallow treads with short risers, both feel wrong — which is why the trade uses proportion rules rather than treating the two dimensions independently.
The best-known is the Blondel rule: two risers plus one tread should total 24 to 25 in (610–635 mm). A 7 in riser with an 11 in tread gives 25 in and feels excellent. A 7.75 in riser with a 10 in tread gives 25.5 in, which is at the steep end but still legal residentially. If your combination falls far outside that band, the stair will feel awkward even if each individual dimension passes code.
Pitch is the angle of the stair, calculated as the arctangent of riser divided by tread. Most comfortable staircases land between 30° and 37°. Below 30° the stair feels shallow and eats floor space; above about 42° it becomes a steep climb that most codes disallow for primary stairs. Ladders and ship's stairs run much steeper and are only permitted for restricted uses such as lofts and access hatches, under specific exceptions.
Headroom is measured vertically from a line drawn along the tread nosings to the ceiling or any obstruction above, and both major US codes require at least 6 ft 8 in. It's easy to overlook when a stair passes under a floor opening or a sloping ceiling, and it's expensive to fix afterwards. Check headroom at the tightest point, which is usually where the stair passes the edge of the upper floor opening — lengthening that opening is the usual remedy.
Stringers are the sloped structural members that carry the treads. A cut stringer has the sawtooth profile notched out of it; a housed stringer has the treads let into routed grooves. The stringer's diagonal length is simply the hypotenuse of the total rise and total run, but you should buy stock longer than the calculated figure to allow for the top and bottom cuts. Typical residential stairs use two or three stringers for a 36 in width, adding more for wider stairs or thinner treads.
The classic cutting technique uses a framing square set with stair gauges at the riser height and tread depth, stepped along the board once per tread. Critically, the bottom of the stringer must be "dropped" by the thickness of the tread material — otherwise the first step ends up one tread thickness taller than the rest, which is precisely the kind of uneven riser that fails inspection.
A landing is a flat platform that interrupts a flight. Codes require one where the vertical rise exceeds around 12 ft, and they are also how you turn a staircase: an L-shaped stair uses a landing to make a 90° turn, and a U-shaped stair uses one to double back 180°. Landings must be at least as deep as the stair is wide, and they are useful for fitting a long stair into a short floor plan — turning the stair rather than steepening it is almost always the better answer when the run doesn't fit.
Winders — tapered treads that turn a corner without a flat landing — save even more space but have stricter rules, since the narrow end of the tread is a fall risk. Where possible, prefer a proper landing.
A handrail is the graspable rail you hold while climbing; a guard is the barrier that stops you falling off the open side. Handrails are typically required on at least one side of any flight with four or more risers, mounted 34 to 38 in above the nosing line, and must be continuous and graspable along the flight. Guards are required where the drop exceeds 30 in, at 36 in high residentially and 42 in commercially, with balusters spaced so that a 4 in sphere cannot pass between them — the rule that keeps small children safe.
Deck stairs are exterior wood stairs, usually with wider treads made from decking boards and slightly taller risers, and they need weather-resistant fasteners and a solid footing at the base. Concrete stairs are formed and poured as a single mass, so the calculation shifts from counting boards to computing the volume of concrete in the stepped profile. Steel stairs use fabricated stringers with bolted or welded treads and are common for access and industrial use. Floating stairs omit risers entirely for a lighter look; they must still satisfy riser and tread rules, and open risers cannot allow a 4 in sphere to pass.
Spiral stairs wind around a central pole and are governed by their own rules, because tread depth varies across the width. The IRC measures the minimum tread depth of 6.75 in at a point 12 in from the narrow edge, allows a taller maximum riser of 9.5 in, and reduces required headroom to 6 ft 6 in. They are a superb space saver — the footprint is just the diameter — but they are hard to carry furniture up and are usually not permitted as the only means of egress from a floor.
Accessible design goes beyond minimum code. Uniform risers and treads, continuous handrails on both sides with extensions past the top and bottom, contrasting nosings that are visible to people with low vision, and avoiding open risers all make a stair usable by more people. Where accessibility is a requirement rather than a preference, the ADA and equivalent standards set specific rules, and a ramp or lift may be needed alongside the stair.
The questions people ask most about stair design. Tap any question to expand.