Stair Calculator
A 9' 0" floor-to-floor rise needs 15 risers of 7 3/16" (182.88 mm) and 14 treads of 10 1/8", a total run of 11' 9 3/4", a stair angle of 35.42° and a stringer 14' 10 3/16" long. Enter your total rise in feet and inches or metric and the calculator picks the number of steps, divides the rise exactly, sizes the treads and checks the result against the figures of the International Residential Code (a model code: your local code and inspector decide what applies, so check with them before you build).
Updated Runs in your browser: nothing you enter is uploadedHow this tool works
Total rise 9' 0" ÷ 15 risers
15 risers of 7 3/16", 14 treads of 10 1/8"
Riser height is shown to the nearest 1/16 inch; the exact height is ≈ 7.2 in (182.88 mm). Mark every riser from the exact figure: 15 rounded risers would be 0.19 in off the total rise. Tread depth was chosen so that 2R + T is about 24 1/2 in, and at least 10 in.
- Total rise
- 9' 0" (2,743.2 mm)
- Risers
- 15
- Treads
- 14 (the top floor is the last step)
- Riser height
- 7 3/16" (182.88 mm)
- Tread depth (set from 2R + T)
- 10 1/8" (257.18 mm)
- Total run
- 11' 9 3/4" (3,600.45 mm)
- Stair angle
- 35.42°
- Stringer length (rise and run, before trimming)
- 14' 10 3/16" (4,526.41 mm)
- 2R + T
- 24.52 in
Check against model-code figures
Figures from the International Residential Code, a model code. Your area may adopt a different edition or change the numbers: this is not a compliance check, so confirm with your local building department before you build.
- WithinRiser height, at most 7 3/4 in (197 mm) (IRC R311.7.5.1). 7 3/16" (182.88 mm) is within that figure.
- WithinTread depth, at least 10 in (254 mm) (R311.7.5.2). 10 1/8" (257.18 mm) is within that figure.
- WithinRise between floors or landings, at most 12 ft 7 in (151 in) (R311.7.3). 9' 0" is within that figure.
- NoteHeadroom, at least 6 ft 8 in (80 in) (R311.7.2). Not checked: enter the clear height you measured, straight up from the line through the nosings.
- WithinComfort rule, 2R + T between 24 and 25 in (a rule of thumb, not code). 2 × 7.2 + 10.13 = 24.52 in is within that range.
- NoteNosing, 3/4 to 1 1/4 in when treads are under 11 in (R311.7.5.3). Not entered: the model code asks for a nosing, or a sloped or beveled riser, when the tread is under 11 in.
Stair figures in the International Residential Code (IRC R311.7)
| What | Model-code figure | IRC section |
|---|---|---|
| Riser height | At most 7 3/4" (197 mm) | R311.7.5.1 |
| Tread depth | At least 10" (254 mm) | R311.7.5.2 |
| Nosing | 3/4" to 1 1/4" (19 to 32 mm) when the tread is under 11" | R311.7.5.3 |
| Headroom | At least 6' 8" (2,032 mm) | R311.7.2 |
| Rise of one flight | At most 12' 7" (3,835 mm) between floors or landings | R311.7.3 |
| Riser and tread variation | No more than 3/8" (9.5 mm) between the largest and smallest in a flight | R311.7.5.1, R311.7.5.2 |
| Comfort rule (not code) | 2 × riser + tread between 24" and 25" | Rule of thumb |
Risers, treads and run for common total rises
| Total rise | Risers | Treads | Riser height | Tread depth | Total run | Angle |
|---|---|---|---|---|---|---|
| 24" | 4 | 3 | 6" | 1' 1/2" | 3' 1 1/2" | 25.64° |
| 30" (a low deck) | 4 | 3 | 7 1/2" | 10" | 2' 6" | 36.87° |
| 36" | 5 | 4 | 7 3/16" | 10 1/8" | 3' 4 1/2" | 35.42° |
| 42" (a porch) | 6 | 5 | 7" | 10 1/2" | 4' 4 1/2" | 33.69° |
| 48" | 7 | 6 | 6 7/8" | 10 13/16" | 5' 4 7/8" | 32.38° |
| 60" | 9 | 8 | 6 11/16" | 11 3/16" | 7' 5 1/2" | 30.79° |
| 8' (96") | 14 | 13 | 6 7/8" | 10 13/16" | 11' 8 9/16" | 32.38° |
| 8' 9" (a basement) | 15 | 14 | 7" | 10 1/2" | 12' 3" | 33.69° |
| 9' (floor to floor) | 15 | 14 | 7 3/16" | 10 1/8" | 11' 9 3/4" | 35.42° |
| 10' | 17 | 16 | 7 1/16" | 10 3/8" | 13' 10" | 34.23° |
How to lay out a stair by hand
- Measure the total rise. Measure from the finished lower floor to the finished upper floor (or the top of the deck boards), straight up. Use the same unit throughout.
- Choose the number of risers. Divide the total rise by a riser height you would like, about 7 inches, and round to a whole number: 108 ÷ 7 = 15.4, so 15 risers.
- Divide the rise exactly. Total rise ÷ number of risers is the riser height: 108 ÷ 15 = 7.2 inches, which is 7 3/16" to the nearest 1/16 inch. Every riser in the flight has the same height.
- Count the treads. There is one tread fewer than risers, because the upper floor is the last step: 15 risers give 14 treads.
- Size the tread and find the run. A comfortable stair has 2 × riser + tread between 24 and 25 inches, so 24.5 − 2 × 7.2 = 10.1 inches, 10 1/8" here. The total run is the tread times the treads: 14 × 10 1/8" = 11' 9 3/4".
- Find the angle and the stringer length. The angle is the arctangent of riser ÷ tread: 35.42°. The stringer is the hypotenuse of the total rise and the total run, √(rise² + run²): 14' 10 3/16" here, before trimming the ends.
Frequently asked questions
- How do you calculate stair rise and run?
- Divide the total rise by a riser height near 7 inches and round to a whole number of risers, then divide the rise by that number for the exact riser. The run of one step is the tread depth and the total run is the tread times the number of treads (one fewer than the risers). A 9' 0" rise gives 15 risers of 7 3/16" (182.88 mm) and a total run of 11' 9 3/4" (3,600.45 mm).
- How many steps do I need for a 9 foot rise?
- About 15 risers with 14 treads at a 7 inch riser: 7 3/16" each, 10 1/8" treads and a run of 11' 9 3/4". If you prefer a lower riser, type 6 1/2" under "Preferred riser height": the calculator then uses 17 risers of 6 3/8": a gentler stair with more steps.
- What is the maximum riser height and minimum tread depth?
- In the International Residential Code, a model code, the riser is at most 7 3/4 inches (197 mm) and the tread at least 10 inches (254 mm), with headroom of at least 6 feet 8 inches. Many places adopt those figures, some change them and commercial buildings follow stricter rules, so check your local code. For example, 12 risers for a 9 ft rise at a 9 inch preferred riser give 9": the tool flags that as outside the 7 3/4 inch figure.
- What is the 2R + T rule for stairs?
- It is a rule of thumb for comfort: twice the riser plus the tread should be between 24 and 25 inches. A 7 3/16" riser with a 10 1/8" tread gives 24.52 in. It is not a code requirement, and the code limits on riser and tread still apply.
- How do you find the stringer length?
- The stringer is the long edge of the board, the hypotenuse of the total rise and the total run: √(rise² + run²). For 9' 0" of rise and 11' 9 3/4" of run that is 14' 10 3/16". The board must be a little longer than this, because the ends are cut square to the floor and the top, and you should plan the cut from a full-size layout. Buy the next standard length up.
- What is a good angle for stairs?
- Most residential stairs are between about 30° and 37°. The default 9 ft stair is 35.42°; a 30 inch deck stair is 36.87° with 4 risers of 7 1/2". The angle comes from the riser and the tread (the arctangent of riser ÷ tread), so a taller riser or a shorter tread makes a steeper stair.
- Why is there one fewer tread than risers?
- The top step is the upper floor itself, so it needs a riser but no tread of its own. A stair with 15 risers has 14 treads: the stringer ends at the upper floor frame.
- Do I subtract the tread thickness from the first riser?
- Usually yes: the stringer is laid out with the same riser everywhere, and the bottom cut is trimmed by the thickness of the tread boards so the first step is the same height as the others once the treads are on. The same applies if the lower floor or the top surface will get a finish. Work from a full-size layout, since the exact method depends on how the treads and floors are built.
- Does the stair calculator work in metric?
- Yes. Type 2700 mm, 270 cm or 2.7 m, or pick millimeters under "Plain numbers are" and type 2700. A 2700 mm rise with a preferred riser of 180 mm gives 15 risers of exactly 180 mm (7 1/16"). Results lead with millimeters, with feet and inches alongside.
- Does this check tell me my stairs will pass inspection?
- No. The checks compare your numbers with figures from the International Residential Code, a model code, and say whether each is within or outside that figure. Your area may adopt another edition or amend it, and the inspector decides. Treat the result as a layout aid and confirm the rules and permits with your local building department.
How it works
The number of risers is the total rise divided by your preferred riser height (7 inches if you leave it empty), rounded to the nearest whole number, and with no preferred riser raised if needed so that no riser passes 7 3/4 inches; there are at least two. The riser is the total rise divided by the number of risers, kept as an exact fraction, and shown to the nearest 1/16 inch and in millimeters, with the rounding difference stated. The treads are one fewer than the risers. If you leave the tread empty it is 24 1/2 inches minus twice the riser, at least 10 inches, rounded to 1/16 inch. The total run is the tread times the treads, the angle is the arctangent of riser ÷ tread, and the stringer length is √(rise² + run²). Tread depth means the horizontal distance from one nosing to the next; a nosing adds to the board, not the run. Lengths are read as exact fractions of an inch (metric uses 1 inch = 25.4 mm exactly). The checks use International Residential Code figures (R311.7): riser at most 7 3/4 inches, tread at least 10 inches, headroom at least 6 feet 8 inches, a flight rise of at most 12 feet 7 inches, and a nosing of 3/4 to 1 1/4 inches when the treads are under 11 inches. The 2R + T range of 24 to 25 inches is a rule of thumb. These are model-code figures, not a statement that a stair complies: local codes differ, and spiral, winder, exterior and commercial stairs follow other rules. Everything runs in your browser.
Sources
More free tools
- Slope CalculatorFind slope from rise and run, or rise or run from a slope: percent, degrees, ratio like 1:12, roof pitch and line length, in feet and inches or metric.
- Feet and Inches CalculatorAdd, subtract, multiply and divide lengths like 5' 7 3/8" with exact fractions, rounded to 1/16 inch, plus decimal feet, mm and cm and a tape view.
- Board Foot CalculatorBoard feet for a whole cut list: pieces × thickness × width × length, 4/4 to 16/4 hardwood or nominal 2×4s, with waste and the cost at your price.
- Voltage Drop CalculatorEstimate voltage drop in volts and percent for copper or aluminum wire, single or three phase, and find the smallest AWG size that stays within 3% or 5%.
- Generator Size CalculatorAdd up running watts and the largest starting surge for the appliances you want to power, and get a generator size with amps at 120 and 240 volts.
- Conduit Fill CalculatorCheck how many wires fit in EMT, rigid, PVC or flexible conduit under NEC Chapter 9: fill percent, pass or fail, and the most of one wire size that fits.
- Deck Stain CalculatorCalculate how many gallons of deck stain you need, based on deck area, number of coats, and waste for touch-ups.
- Concrete Footing CalculatorConcrete for deck, fence and wall footings in cubic yards and 80 lb bags, plus a Sonotube chart. A 10 ft × 12 in × 8 in footing needs 13 bags.
- Fence CalculatorPickets, posts, rails and bags of concrete for a wood fence from its length, height, post spacing, gates and picket gap, with a picket gap table.
- Deck Boards CalculatorDeck boards, board length, joists and screws or clips for a deck from its size, board width, gap and length, with offcut reuse, diagonal lay and tables.
- Concrete Steps CalculatorCubic yards and bags of concrete for solid steps from the number of steps, riser, tread and width, with an optional landing at the top. Inches or metric.
- Baluster Spacing CalculatorBalusters per rail section, the equal gap, on-center spacing and the first baluster’s position from the section length, baluster width and largest gap.