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Stair Calculator

Calculate stair dimensions, riser heights, tread depths, stringer lengths and stair pitch. Includes recommendations for residential and commercial building codes.

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Select a calculation mode and enter dimensions to solve the stair configuration.

Dimension Specifications

Select a Building Type for guidance
Stair Design Recommendations
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Stair Geometry Diagram
Total RiseTotal RunRiserTreadAngleStringer

Ready to Calculate

Select a calculation mode, fill in the stair specifications, and click Calculate to view the layout results.

Formula Details

Select a calculation mode above to display its corresponding geometry formula and variables, or browse the specific calculations below:

Calculation Example

Worked Example
Scenario

Residential Staircase: Calculate dimensions for a home staircase with a vertical rise of 2.70 meters (approx. 9 ft), using a target riser height of 180 mm and a standard 267 mm tread depth.

Calculation Steps
  1. 1.Select Total Rise + Riser Height mode and toggle Metric unit system. Input Total Rise = 2.70 m, Preferred Riser = 180 mm, Desired Tread = 267 mm.
    Total Rise = 2.70 m, Riser = 180 mm, Tread = 267 mm
  2. 2.Solve steps count by dividing total rise by target riser height and rounding.
    Steps = round(2.70 m / 0.18 m) = 15 steps
  3. 3.Calculate actual riser height and tread count.
    Actual Riser = 2.70 m / 15 = 180.0 mm | Treads = 15 - 1 = 14 treads
  4. 4.Compute total horizontal run and stringer length.
    Total Run = 14 × 267 mm = 3.738 m | Stringer = √(2.70² + 3.738²) = 4.61 m
  5. 5.Find stair angle (pitch).
    Angle = arctan(2.70 / 3.738) = 35.84°
Final Quantity Needed15 Steps, Actual Riser: 180.0 mm, Actual Tread: 267.0 mm, Total Run: 3.74 m, Stair Pitch: 35.8°, Stringer Length: 4.61 m
Worked Example
Scenario

Outdoor Deck Stairs: Build wooden deck stairs with a total rise of 4.5 feet (54 inches) using comfortable riser/tread metrics (7 in riser, 11 in tread).

Calculation Steps
  1. 1.Select Total Rise + Riser Height mode, toggle Imperial unit system. Set Total Rise = 4.5 ft, Preferred Riser = 7 in, Desired Tread = 11 in.
    Total Rise = 54 in, Riser = 7 in, Tread = 11 in
  2. 2.Find the step count.
    Steps = round(54 in / 7 in) = 8 steps
  3. 3.Compute actual step riser height and tread count.
    Actual Riser = 54 in / 8 = 6.75 in | Treads = 8 - 1 = 7 treads
  4. 4.Calculate total horizontal run, stringer length, and pitch angle.
    Total Run = 7 × 11 in = 77.0 in (6.42 ft) | Stringer = √(54² + 77²) = 94.05 in (7.84 ft) | Angle = 35.04°
Final Quantity Needed8 Steps, Riser Height: 6.75 in, Tread Depth: 11.00 in, Total Run: 6.42 ft, Stair Pitch: 35.0°, Stringer Length: 7.84 ft
Worked Example
Scenario

Commercial Staircase: Formulate a commercial egress stair with a vertical rise of 3.20 meters, adhering to IBC/ADA guidelines (riser max 180 mm, tread min 280 mm).

Calculation Steps
  1. 1.Select Total Rise + Riser Height mode, building type = Commercial, Metric system. Set Total Rise = 3.20 m, Preferred Riser = 170 mm, Desired Tread = 280 mm.
    Total Rise = 3.20 m, Riser = 170 mm, Tread = 280 mm
  2. 2.Calculate steps and check code compliance.
    Steps = round(3.20 m / 0.17 m) = 19 steps | Riser = 3.20 m / 19 = 168.4 mm (< 180 mm, OK)
  3. 3.Verify tread count and total run.
    Treads = 18 | Total Run = 18 × 280 mm = 5.04 m | Tread = 280.0 mm (>= 280 mm, OK)
  4. 4.Compute stringer length and pitch.
    Stringer = √(3.20² + 5.04²) = 5.97 m | Pitch = 32.41° (< 34°, OK)
Final Quantity Needed19 Steps, Riser Height: 168.4 mm, Tread Depth: 280.0 mm, Total Run: 5.04 m, Stair Pitch: 32.4°, Stringer Length: 5.97 m (Fully Compliant)

How to Use

Follow these simple steps to solve and layout any staircase structure:

  1. Select the desired calculation mode: Choose between Rise + Riser Height, Rise + Step Count, Rise + Total Run, or Custom Stair Design.
  2. Enter the required dimensions: Provide measurements in the dynamic inputs fields. Only inputs relevant to your mode will appear.
  3. Choose the preferred unit system: Toggle between Imperial (ft/in) and Metric (m/cm/mm) at the top right of the form.
  4. Optionally select the building type: Select Residential, Commercial, Outdoor, or Deck to see live design guidelines recommendations.
  5. Click Calculate: Click the Calculate button to process your dimensions.
  6. Review the results: Check the step count, actual riser height, tread depth, total run, angle pitch, and stringer length in the results section, along with code warnings.

Frequently Asked Questions

How do I calculate the number of stair steps?
Divide the total vertical rise of the stairs by your preferred riser height (usually between 7 and 7.75 inches for residential stairs). Round the resulting number to the nearest whole step count. For example, a vertical rise of 84 inches divided by a 7.25-inch riser yields 11.58 steps. Rounding up gives 12 steps. The actual riser height is then 84 / 12 = 7 inches.
What is a comfortable riser height?
For residential stairs, a comfortable riser height is typically between 7 and 7.75 inches (175–196 mm), with 7 inches being the traditional ideal. For commercial public staircases, building codes generally enforce a maximum riser height of 7 inches (180 mm) and minimum of 4 inches (100 mm) to maximize accessibility.
What is the ideal stair angle?
The ideal angle of inclination (pitch) for standard staircases ranges between 30° and 37°. Angles shallower than 20° are too flat and are better suited for ramps. Angles steeper than 45° are too steep, making descent dangerous, and are classified as ladders.
How is stringer length calculated?
The stair stringer length is the diagonal length of the support board that runs beneath the steps. It represents the hypotenuse of the right triangle formed by the total rise and total run. It is calculated using the Pythagorean theorem: Stringer Length = √(Total Rise² + Total Run²).
Can I switch between Metric and Imperial?
Yes, you can toggle between Imperial (in/ft) and Metric (mm/cm/m) at the top right of the calculator card. The input placeholders, labels, and results conversions will dynamically update.
How accurate are the calculations?
The calculations are mathematically precise. However, during installation, builders must account for exact lumber thickness, landing levels, and tread thickness variations. Always confirm stair layout plans with a professional builder or structural inspector.

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Disclaimer

Calculations are estimates based on the values you enter and standard engineering formulas. Results are intended for planning and estimation only. Always verify critical measurements, specifications, and local building requirements before purchasing materials or beginning construction.