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StairCalculator.appCalculate Stairs

Stair Calculator

Calculate stair rise, run, tread depth, riser height, stair angle and stringer length instantly.

Enter your floor-to-floor height and a target riser height. Results, a dimensioned stair diagram and a stringer cut layout update as you type. Works in feet and inches (with fractions) or metric.

Calculator mode

Rise, run, riser count, tread count, riser height, tread depth, angle and stringer length.

Stair dimensions

7 1/4 in target riser, 10 1/2 in tread, 1 in nosing. A common interior starting point.

Affects warnings and recommendations only. Local building regulations control.

Layout

One straight flight from floor to floor.

Total rise

Vertical distance from the finished lower floor to the finished upper floor, e.g. 9 ft 2 in, 110, or 110 1/2.

Risers

The riser height you would like. The calculator rounds to a whole number of equal risers.

Treads & run

Horizontal distance from one riser face to the next, measured nosing to nosing. Do not include the nosing overhang.

Tread overhang beyond the riser below. Enter 0 for none.

Results

Updates instantly as you type

With a total rise of 108″ and 15 risers, the calculated riser height is 7 3/16″. 14 treads of 10 1/2″ give a total run of 147″, a stair angle of 34.4° and a stringer length of 182 7/16″.

Primary results

RisersCalculated
15
TreadsCalculated
14
Riser heightCalculated
7 3/16″7.2 in
Tread depthYour input
10 1/2″10.5 in
Total runCalculated
12′ 3″147″
Stair angleCalculated
34.4°
Stringer lengthCalculated
15′ 2 7/16″182 7/16″
Total riseYour input
9′ 0″108″

With a total rise of 108″ and 15 risers, the calculated riser height is 7 3/16″. 14 treads of 10 1/2″ give a total run of 147″, a stair angle of 34.4° and a stringer length of 182 7/16″.

Construction measurements

Construction measurements
Actual rise (risers × riser height)108″Calculated
Horizontal run (treads × tread depth)147″Calculated
Footprint incl. bottom nosing148″Calculated
Tread board depth (tread + nosing)11 1/2″Calculated
Nosing / overhang1″Your input
Number of steps (risers)15Calculated
Framing square settings (rise on tongue / run on blade)7 3/16″ / 10 1/2″Calculated
Step hypotenuse (nosing to nosing)12 3/4″Calculated
Stringer layout length182 7/16″Calculated
Nosing line to floor (risers × step hypotenuse)191″Calculated
Top plumb cut7 3/16″Calculated
Bottom riser cut (rise − 1″ drop)6 3/16″Calculated
Notch depth (perpendicular)5 15/16″Calculated
Stringer throat remaining5 5/16″Calculated
Minimum stringer board length198 11/16″nosing line 191″ + plumb cut 7 11/16″Calculated
Stringer board2x12 × 18′ 0″shortest standard length ≥ 198 11/16″Recommended
Riser rounded to 1/16 in7 3/16″× 15 risers = 3/16″ underCalculated
Handrail rake length (no extensions)15′ 2 7/16″with one-tread level extensions: 16′ 11 7/16″Calculated
Balusters at 1 1/4″ wide2 per tread · 28 totalgap 4″ · guard required on open sidesCalculated
Stair width36″Your input
Riser + tread17 11/16″target ≈ 17–18 inCalculated
2 × riser + tread24 7/8″target ≈ 24–25 inCalculated

Design checks — IRC-style

  • Good: Geometry within selected target range

    Your stair geometry is within the IRC-style reference values selected. Local building regulations control.

  • Note: Layout rounding note

    Marking every riser at 7 3/16″ makes the stair 3/16″ too short over 15 risers. Lay out from cumulative heights (riser × step number) on a story pole, or step off with dividers, so the error does not build up.

  • Note: Guard needed on open sides

    Total rise 108″ exceeds 30″: any open side needs a guard (commonly ≥ 36″ on a stair) with openings that stop a 4″ sphere — 2 balusters per tread at 1 1/4″ wide leaves a 4″ gap.

Important: Building codes vary by location. Always verify your final stair design against the applicable local building code and authority having jurisdiction.

Recommendations

  • Stringer material

    Lay out 15 notches on a 2x12. The nosing line is 15′ 11″ long and the top plumb cut adds 7 11/16″, so the board must be at least 16′ 6 11/16″; 18′ 0″ is the shortest standard stock length.

Compare riser counts

Same total rise — see how one riser more or fewer changes the stair.

RisersRiser heightTreadTotal runAngleChecks
147 11/16″10 1/2″136 1/2″36.3°within range
15current7 3/16″10 1/2″147″34.4°within range
166 3/4″10 1/2″157 1/2″32.7°within range
176 3/8″10 1/2″168″31.2°within range

Materials estimate

4 stringers · 14 treads · 15 risers · width 36″

2x12 stringers, flight 1Layout length 15′ 2 7/16″ + cut allowance4 × 18′ 0″
Tread boards11 1/2″ deep × 1″ thick (going + nosing)14 × 36″
Riser boards7 3/16″ tall15 × 36″
Stringer hangers / connectorsTop connection; add a kicker or base plate at the bottom.4 pcs
Structural screws (approx.)3 per tread and 2 per riser at each stringer, rounded up.300 pcs

Take-off quantities before waste. Confirm spans and connections with your local requirements.

Printed from StairCalculator.app · Reference profile: IRC-style residential reference (US)

Computed at full precision from the entered measurements and rounded for display only. Building codes are adopted locally; confirm the reference limits used against the code in force at the project location.

Method

How Stair Calculations Work

To calculate stairs, divide the total floor-to-floor rise by the desired riser height to determine the number of risers. Then divide the total rise by the number of risers to determine the actual riser height. From there, a chosen tread depth and the number of treads determine the total run, the stair angle, and the stringer length.

  1. Step 1

    Measure the total rise

    Total rise = finished floor (upper) − finished floor (lower)

    Example: a floor-to-floor height of 108 in.

  2. Step 2

    Determine the number of risers

    Risers = round(total rise ÷ target riser height)

    Example: round(108 ÷ 7.25) = round(14.9) = 15 risers.

  3. Step 3

    Calculate the actual riser height

    Riser height = total rise ÷ risers

    Example: 108 ÷ 15 = 7.2 in per riser.

  4. Step 4

    Determine the tread depth

    Tread depth = chosen depth, or available run ÷ tread count

    Example: a 10.5 in tread depth is chosen for comfort.

  5. Step 5

    Calculate the total run

    Total run = treads × tread depth

    Example: 14 treads × 10.5 in = 147 in of total run.

  6. Step 6

    Calculate the stair angle

    Angle = arctan(riser height ÷ tread depth)

    Example: arctan(7.2 ÷ 10.5) ≈ 34.4 degrees.

  7. Step 7

    Calculate the stringer length

    Stringer = √(total rise² + total run²)

    Example: √(108² + 147²) ≈ 182.4 in.

  8. Step 8

    Check dimensions against applicable requirements

    Compare riser, tread, headroom and width against local code

    Example: compare 7.2 in riser and 10.5 in tread against your local code before building.

Key terms

Total rise
The full vertical distance from the lower finished floor to the upper finished floor.
Total run
The full horizontal distance the stair covers, equal to the number of treads times the tread depth.
Riser
The vertical face of a single step; riser height is total rise divided by the number of risers.
Tread
The horizontal surface of a single step that you stand on; tread depth is measured front to back.
Nosing
The small overhang of a tread beyond the riser below it, which adds usable foot space without adding to the total run.
Stringer
The angled structural board that supports the treads and risers along the slope of the stair.
Stair angle
The slope of the stair in degrees, calculated as arctan(riser height ÷ tread depth).
Headroom
The clear vertical distance measured from the nosing line of a tread up to the ceiling or framing above.
Floor-to-floor height
Another name for total rise: the vertical distance between two finished floor levels connected by the stair.

About Stair Calculations

Every stair calculation is built from two related sums. The number of risers multiplied by the riser height always equals the total rise, and the number of treads multiplied by the tread depth always equals the total run. Because the riser count must be a whole number, the actual riser height is almost always a slightly different value than the target riser height you started with, which is why the calculator rounds the riser count first and then recalculates the exact riser height.

Riser and tread dimensions are also related by long-standing comfort rules of thumb rather than a single fixed rule: riser height plus tread depth is commonly targeted around 17 to 18 in, and twice the riser height plus the tread depth (sometimes called the Blondel formula) is commonly targeted around 24 to 25 in. These are guidelines for comfortable stride length, not code requirements, and they can be overridden by the applicable building code.

The stair angle ties riser height and tread depth together trigonometrically. Interior stairs typically land in a 30 to 37 degree range: shallower angles use more floor space but feel easier to climb, while steeper angles save space but feel closer to a ladder. Reference maximum angles differ between residential and commercial code profiles, and local amendments can differ further.

Reference

Stair Formulas

The formulas below drive every result in the calculator above. Each includes a one-line explanation and a worked example using the same numbers throughout for easy comparison.

Number of Risers

risers = round(total rise ÷ target riser height)

The total rise is divided by a target riser height and rounded to the nearest whole riser.

round(108 ÷ 7.25) = round(14.9) = 15 risers.

Riser Height

riser height = total rise ÷ risers

Once the riser count is fixed, the total rise is redistributed evenly across every riser.

108 ÷ 15 = 7.2 in per riser.

Number of Treads

treads = risers − 1 (flush top)

When the upper floor serves as the last step, the tread count is one less than the riser count.

15 risers − 1 = 14 treads.

Total Run

total run = treads × tread depth

Total run is the horizontal distance covered by the stair, from the chosen tread depth.

14 × 10.5 in = 147 in.

Stair Angle

angle = arctan(riser height ÷ tread depth)

The stair angle in degrees comes from the ratio of riser height to tread depth.

arctan(7.2 ÷ 10.5) ≈ 34.4°.

Stringer Length

stringer = √(total rise² + total run²)

The stringer spans the hypotenuse of the triangle formed by total rise and total run.

√(108² + 147²) ≈ 182.4 in.

Rise/Run Comfort Check

riser + tread ≈ 17–18 in; 2×riser + tread ≈ 24–25 in

These comfort rules of thumb help judge whether a riser/tread combination feels comfortable to climb.

7.2 + 10.5 = 17.7 in; 2(7.2) + 10.5 = 24.9 in — both within the common comfort range.

Headroom

headroom = opening length × (riser ÷ tread) − upper floor thickness

Headroom estimates the clear vertical space below a floor opening along the slope of the stair.

60 in × (7.2 ÷ 10.5) − 10 in ≈ 31.1 in of headroom at that point.

Stringer Bottom Cut

bottom riser cut = riser height − tread thickness

The bottom of the stringer is trimmed by the tread's thickness so the first step matches the height of the rest.

7.2 in riser − 1 in tread thickness = 6.2 in bottom riser cut.

Commonly cited reference values

These are commonly cited reference values, not universal requirements. Local codes control; always verify with the applicable local building authority.
DimensionIRC-style residentialIBC-style commercial
Maximum riser height7.75 in7 in
Minimum riser height—4 in
Minimum tread depth10 in11 in
Maximum riser variation0.375 in0.375 in
Minimum headroom80 in80 in
Minimum stair width36 in44 in
Maximum stair angle42°33°

Worked math

Worked Stair Examples

The examples below are illustrative calculations, not building code requirements. They show the exact arithmetic behind each result so you can check the same math against your own measurements.

7 ft floor-to-floor height

Inputs for 7 ft floor-to-floor height
Total rise84 in (7 ft)
Target riser height7.25 in
Tread depth10.5 in
Top stepFlush with upper floor

Steps

  1. Risers = round(84 ÷ 7.25) = round(11.59) = 12
  2. Riser height = 84 ÷ 12 = 7.000 in
  3. Treads = 12 − 1 = 11
  4. Total run = 11 × 10.5 = 115.5 in
  5. Stair angle = arctan(7.000 ÷ 10.5) ≈ 33.7°
  6. Stringer length = √(84² + 115.5²) ≈ 142.8 in

Results

Results for 7 ft floor-to-floor height
Risers12
Riser height7 in (7.000 in)
Treads11
Total run115 1/2 in (115.5 in)
Stair angle≈ 33.7°
Stringer length≈ 142 13/16 in (142.82 in)

This example is illustrative only; verify the final riser and tread dimensions against your local code before building.

8 ft floor-to-floor height

Inputs for 8 ft floor-to-floor height
Total rise96 in (8 ft)
Target riser height7.25 in
Tread depth10.5 in
Top stepFlush with upper floor

Steps

  1. Risers = round(96 ÷ 7.25) = round(13.24) = 13
  2. Riser height = 96 ÷ 13 ≈ 7.385 in
  3. Treads = 13 − 1 = 12
  4. Total run = 12 × 10.5 = 126 in
  5. Stair angle = arctan(7.385 ÷ 10.5) ≈ 35.1°
  6. Stringer length = √(96² + 126²) ≈ 158.4 in

Results

Results for 8 ft floor-to-floor height
Risers13
Riser height7 3/8 in (7.385 in)
Treads12
Total run126 in (126.0 in)
Stair angle≈ 35.1°
Stringer length≈ 158 7/16 in (158.40 in)

This example is illustrative only; verify the final riser and tread dimensions against your local code before building.

9 ft floor-to-floor height

Inputs for 9 ft floor-to-floor height
Total rise108 in (9 ft)
Target riser height7.25 in
Tread depth10.5 in
Top stepFlush with upper floor

Steps

  1. Risers = round(108 ÷ 7.25) = round(14.90) = 15
  2. Riser height = 108 ÷ 15 = 7.200 in
  3. Treads = 15 − 1 = 14
  4. Total run = 14 × 10.5 = 147 in
  5. Stair angle = arctan(7.200 ÷ 10.5) ≈ 34.4°
  6. Stringer length = √(108² + 147²) ≈ 182.4 in

Results

Results for 9 ft floor-to-floor height
Risers15
Riser height7 3/16 in (7.200 in)
Treads14
Total run147 in (147.0 in)
Stair angle≈ 34.4°
Stringer length≈ 182 7/16 in (182.41 in)

This example is illustrative only; verify the final riser and tread dimensions against your local code before building.

10 ft floor-to-floor height

Inputs for 10 ft floor-to-floor height
Total rise120 in (10 ft)
Target riser height7.25 in
Tread depth10.5 in
Top stepFlush with upper floor

Steps

  1. Risers = round(120 ÷ 7.25) = round(16.55) = 17
  2. Riser height = 120 ÷ 17 ≈ 7.059 in
  3. Treads = 17 − 1 = 16
  4. Total run = 16 × 10.5 = 168 in
  5. Stair angle = arctan(7.059 ÷ 10.5) ≈ 33.9°
  6. Stringer length = √(120² + 168²) ≈ 206.5 in

Results

Results for 10 ft floor-to-floor height
Risers17
Riser height7 1/16 in (7.059 in)
Treads16
Total run168 in (168.0 in)
Stair angle≈ 33.9°
Stringer length≈ 206 7/16 in (206.46 in)

This example is illustrative only; verify the final riser and tread dimensions against your local code before building.

Deck stairs, 48 in deck height

Inputs for Deck stairs, 48 in deck height
Deck height (grade to deck surface)48 in
Target riser height7 in
Tread depth11 in
Top stepFlush (deck surface is the top step)

Steps

  1. Risers = round(48 ÷ 7) = round(6.86) = 7
  2. Riser height = 48 ÷ 7 ≈ 6.857 in
  3. Treads = 7 − 1 = 6
  4. Total run = 6 × 11 = 66 in
  5. Stair angle = arctan(6.857 ÷ 11) ≈ 31.9°
  6. Stringer length = √(48² + 66²) ≈ 81.6 in

Results

Results for Deck stairs, 48 in deck height
Risers7
Riser height≈ 6 7/8 in (6.857 in)
Treads6
Total run66 in (66.0 in)
Stair angle≈ 31.9°
Stringer length≈ 81 5/8 in (81.61 in)

Deck stairs are typically measured from finished grade or the landing surface, and outdoor exposure conditions may add local requirements beyond dimensions alone.

Metric example, 2700 mm floor-to-floor

Inputs for Metric example, 2700 mm floor-to-floor
Total rise2700 mm
Target riser height180 mm
Tread depth270 mm
Top stepFlush with upper floor

Steps

  1. Risers = round(2700 ÷ 180) = round(15.0) = 15
  2. Riser height = 2700 ÷ 15 = 180.0 mm
  3. Treads = 15 − 1 = 14
  4. Total run = 14 × 270 = 3780 mm
  5. Stair angle = arctan(180 ÷ 270) ≈ 33.7°
  6. Stringer length = √(2700² + 3780²) ≈ 4645 mm

Results

Results for Metric example, 2700 mm floor-to-floor
Risers15
Riser height180 mm
Treads14
Total run3780 mm
Stair angle≈ 33.7°
Stringer length≈ 4645 mm

Metric stair dimensions follow the same formulas as imperial ones; only the unit of measure changes.

Field measurements

Stair Measurement Guide

Accurate stair calculations depend on accurate field measurements. Use these notes to measure each dimension correctly and avoid the most common errors that throw off a stair layout.

Total rise

How to measure

  • Measure from the finished surface of the lower floor to the finished surface of the upper floor, not from subfloor to subfloor.
  • Account for any finish flooring, such as tile or hardwood, that will be added later on both levels.
  • Measure with a laser level or a straight, plumb reference rather than along a sloped surface.

Common mistakes

  • Measuring only to the subfloor and forgetting to add planned finish flooring thickness.
  • Taking a single measurement when the framing is slightly uneven; measure at both ends of the stair opening.

Total run

How to measure

  • Measure the horizontal distance available for the stair, from the face of the bottom riser to the face of the top riser or wall.
  • Check the run at floor level and confirm nothing (ductwork, framing, doors) intrudes into the space above.

Common mistakes

  • Forgetting to leave clearance for a door swing or landing at the bottom of the stair.
  • Not verifying the run against the tread count once the riser height is finalized.

Floor thickness

How to measure

  • Measure the full assembly thickness of the upper floor: joist depth, subfloor, and finish flooring.
  • Use this figure when calculating headroom at the stair opening, since it reduces the clear height below the framing.

Common mistakes

  • Using only the joist depth and ignoring subfloor and finish flooring thickness.
  • Assuming the same floor thickness throughout the house without checking at the actual stair location.

Tread

How to measure

  • Measure tread depth from the face of one riser to the face of the next, excluding nosing overhang.
  • Measure tread board thickness separately; it affects the bottom riser cut on the stringer.

Common mistakes

  • Confusing tread depth (front to back) with tread width (side to side, generally the stair width).
  • Including the nosing overhang in the tread depth used for the total run calculation.

Riser

How to measure

  • Measure riser height as the vertical distance from the top of one tread to the top of the next.
  • Use a level and a straight edge to confirm each riser is close to identical along the run of the stair.

Common mistakes

  • Allowing the first or last riser to differ from the rest because of finish flooring added after framing.
  • Rounding riser heights loosely instead of recalculating the exact value from the total rise.

Nosing

How to measure

  • Measure nosing as the horizontal projection of the tread beyond the face of the riser below it.
  • Keep nosing projection consistent from step to step, including at the top and bottom of the flight.

Common mistakes

  • Adding nosing to the total run calculation instead of treating it as extra tread overhang.
  • Using an oversized nosing that creates a trip hazard or an undersized nosing at the top landing.

Headroom

How to measure

  • Measure headroom vertically from the nosing line of each tread up to the underside of the ceiling or header above.
  • Check headroom at multiple points along the stair, since it is often smallest partway up the flight, not just at the bottom.

Common mistakes

  • Measuring headroom only at the bottom step and missing a lower point further up the stair.
  • Forgetting to subtract the thickness of the upper floor framing from the available headroom.

Questions

Stair Calculator FAQ

Answers to common questions about stair rise, run, risers, treads, stringers, and how they relate to building codes.

What is a stair calculator?

A stair calculator is a tool that converts a floor-to-floor height into a buildable set of stair dimensions. You enter the total rise and a target riser height, and it works out the number of risers, the actual riser height, the number of treads, the total run, the stair angle, and the stringer length. It removes the trial-and-error of dividing a rise by hand and checking the remainder.

How do I calculate stairs?

Start by measuring the total rise (finished floor to finished floor). Divide the total rise by your target riser height and round to the nearest whole number to get the number of risers, then divide the total rise by that riser count to get the actual riser height. Pick a tread depth, multiply it by the number of treads (risers minus 1 for a flush top) to get the total run, and use those two numbers to find the stair angle and stringer length.

How many risers do I need?

The number of risers equals the total rise divided by your target riser height, rounded to the nearest whole number. For example, an 84 in total rise with a 7.25 in target riser gives 84 ÷ 7.25 = 11.6, which rounds to 12 risers. The riser height is then recalculated as 84 ÷ 12 = 7.0 in exactly, so every riser in the flight is identical.

How do I calculate stair rise and run?

Total rise is the vertical floor-to-floor height; total run is the horizontal distance the stair covers. Divide total rise by the number of risers to get the riser height, and multiply the number of treads by the tread depth to get the total run. For a 108 in rise with 15 risers of 7.2 in and 14 treads of 10.5 in, the total run is 14 × 10.5 = 147 in.

How do I calculate stair angle?

Stair angle in degrees equals the arctangent of riser height divided by tread depth: angle = arctan(rise ÷ run). Using a 7.2 in riser and a 10.5 in tread, arctan(7.2 ÷ 10.5) is about 34.4 degrees. Most interior stairs fall in the 30 to 37 degree range; steeper angles feel more like a ladder and shallower angles need more floor space.

How deep should a stair tread be?

IRC-style residential reference values commonly cite a 10 in minimum tread depth, while IBC-style commercial reference values commonly cite 11 in as a minimum. Many builders target 10.5 to 11.5 in for comfortable footing. Local codes control the actual minimum in your jurisdiction, so always confirm before finalizing a design.

How high should a stair riser be?

A common target for residential stairs is around 7 to 7.75 in, with IRC-style reference values commonly citing 7 3/4 in as a maximum. IBC-style commercial reference values commonly cite a 7 in maximum and a 4 in minimum. All risers in a single flight should be as close to identical as possible, since uneven risers are a common trip hazard.

How do I calculate stringer length?

Stringer length is the hypotenuse of a right triangle formed by the total rise and total run: stringer = √(rise² + run²). For a 108 in rise and a 147 in run, the stringer length is √(108² + 147²) ≈ 182.4 in. Add extra board length for the bottom riser cut and top plumb cut when ordering lumber.

How many treads do stairs need?

When the upper floor acts as the final step (a flush top), the number of treads equals the number of risers minus one. A stair with 15 risers has 14 treads, because the last riser lands you on the upper floor itself rather than on another tread.

How do I calculate stairs for a deck?

Measure the deck height from finished grade (or the landing surface) up to the top of the decking, then treat that as the total rise with a flush top, since the deck surface serves as the top step. For a 48 in deck height with a 7 in target riser, 48 ÷ 7 rounds to 7 risers, giving an actual riser height of 48 ÷ 7 ≈ 6 7/8 in and 6 treads.

How do I calculate a stair stringer?

First calculate the riser height, tread depth, riser count, and tread count for the flight. The stringer's overall layout length is √(total rise² + total run²). The bottom riser cut is shortened by the tread's board thickness (riser height minus tread thickness) so the first step above the floor matches the height of the rest.

How do I calculate total stair run?

Total run equals the number of treads multiplied by the tread depth. With 14 treads at 10.5 in each, the total run is 14 × 10.5 = 147 in, or 12.25 ft. This is the horizontal floor space the stair will occupy, not counting any nosing overhang.

How do I calculate stairs from floor to floor height?

Floor-to-floor height is simply the total rise. Measure from the finished surface of the lower floor to the finished surface of the upper floor, then divide by your target riser height and round to get the number of risers, exactly as with any other stair calculation. For a 9 ft (108 in) floor-to-floor height and a 7.25 in target riser, you get 15 risers at 7.2 in each.

What is the ideal stair angle?

There is no single universally ideal stair angle, but interior stairs are commonly built in the 30 to 37 degree range, with roughly 32 to 35 degrees considered comfortable for everyday use. Angles below about 30 degrees require more horizontal space; angles above about 40 degrees start to feel steep and are typically reserved for utility or attic stairs where codes allow it.

What is the difference between rise and run?

Rise is the vertical measurement: the height of one riser, or the total floor-to-floor height when referring to total rise. Run is the horizontal measurement: the depth of one tread, or the total horizontal distance the stair covers when referring to total run. Stair angle relates the two through arctan(rise ÷ run).

How many stairs do I need for a 7-foot height?

A 7 ft (84 in) floor-to-floor height with a 7.25 in target riser gives 84 ÷ 7.25 = 11.6, which rounds to 12 risers. Recalculating, 84 ÷ 12 = 7.0 in exactly, so you would build 12 risers of 7 in each with 11 treads.

How many stairs do I need for an 8-foot height?

An 8 ft (96 in) floor-to-floor height with a 7.25 in target riser gives 96 ÷ 7.25 ≈ 13.24, which rounds to 13 risers. Recalculating, 96 ÷ 13 ≈ 7.385 in, which is about 7 3/8 in, with 12 treads.

How many stairs do I need for a 9-foot height?

A 9 ft (108 in) floor-to-floor height with a 7.25 in target riser gives 108 ÷ 7.25 ≈ 14.9, which rounds to 15 risers. Recalculating, 108 ÷ 15 = 7.2 in, which is about 7 3/16 in, with 14 treads.

How many stairs do I need for a 10-foot height?

A 10 ft (120 in) floor-to-floor height with a 7.25 in target riser gives 120 ÷ 7.25 ≈ 16.55, which rounds to 17 risers. Recalculating, 120 ÷ 17 ≈ 7.0588 in, which is about 7 1/16 in, with 16 treads.

How do I calculate stairs in inches?

Enter every measurement, total rise, target riser height, and tread depth, in inches and the same formulas apply directly: risers = round(total rise ÷ target riser height), riser height = total rise ÷ risers, total run = treads × tread depth. Inches are the most common unit for stair layout in the United States because riser and tread dimensions are typically specified to the nearest 1/16 in.

How do I calculate stairs in feet?

If your floor-to-floor height is given in feet, convert it to inches first (multiply by 12) so it matches the riser and tread dimensions typically used in stair layout, then apply the standard formulas. A 9 ft height becomes 108 in, giving 15 risers of 7.2 in at a 7.25 in target.

Can I calculate stairs in metric?

Yes. The same formulas work in millimeters or meters; only the units change. For a 2700 mm floor-to-floor height with a 180 mm target riser, 2700 ÷ 180 = 15 risers exactly, giving 14 treads at 270 mm each for a total run of 3780 mm and a stair angle of about 33.7 degrees.

How accurate is a stair calculator?

A stair calculator is as accurate as arithmetic allows, the formulas are exact, so results reflect the numbers you enter precisely. Accuracy in the field also depends on how carefully you measure total rise, account for finished flooring thickness on both levels, and cut materials to the calculated dimensions.

Do stair calculations need to follow building codes?

The arithmetic of stair calculation is universal, but the resulting dimensions must still satisfy the building code adopted in your jurisdiction, which can vary by state, city, or occupancy type. This tool references commonly cited IRC-style and IBC-style values for context, but it is not a substitute for checking with your local building department or a qualified professional before construction.

Focused tools

More Stair Calculators

Need one specific answer? These 40 pages each pair a purpose-built calculator with a short, practical guide: stringers, deck stairs, landings and turns, angle and slope, railings, concrete, carpet and more.

Stringers

Deck & outdoor stairs

Materials

Landings, turns & shapes

Rise, run & dimensions

Angle & slope

Design, layout & building

Metric & regional

Railings, balusters & flooring

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Accuracy & responsibility

Accuracy statement

StairCalculator.app is a professional stair layout tool. Every result is computed with full floating-point precision from the standard stair formulas (riser height = total rise ÷ risers; run = treads × tread depth; angle = arctan(rise ÷ run); stringer = √(rise² + run²)) and rounded only for display, to 1/16 in or 1 mm. The calculation engine is covered by automated tests and produces the same numbers a framing square, calculator or CAD package will.

Results are exactly as accurate as the measurements entered. Measure total rise finished floor to finished floor, at the point where the stair actually lands, and confirm tread thickness and stringer stock before cutting. Building codes are adopted locally and differ between jurisdictions; the IRC, IBC and UK reference limits shown are provided for checking your design, and the authority having jurisdiction has the final say.