Stair CalculatorFree online other calculator — instant results, no sign-up
Number of steps, riser and tread for stairs.
About the Stair Calculator
The Stair Calculator determines the number of steps, exact riser height, total horizontal run, and incline angle required for a straight flight of stairs based on vertical elevation. Builders, carpenters, and DIY renovators use it to plan stair layout dimensions that fit within available floor space while maintaining a consistent step height.
- Total rise
- The total vertical distance from the finished lower floor surface to the finished upper floor surface, measured in centimeters (typically 50 to 400 cm).
- Target riser
- The desired height for each individual step riser, in centimeters (residential stairs typically target 17 to 20 cm).
- Tread depth
- The horizontal depth of each step tread, measured in centimeters (commonly between 25 and 30 cm).
Formula and method
Number of risers (k) = round(h / r) Actual riser = h / k Total run = (k − 1) × t Angle = arctan(Actual riser / t) × (180 / π)
- hTotal rise (total vertical height of the staircase)
- rTarget riser height
- tTread depth
- kComputed integer count of risers
The tool divides the total rise by the target riser height and rounds to the nearest integer to establish the total number of risers. The total rise is then divided by this integer count to yield the exact uniform riser height. Total horizontal run is calculated for k - 1 treads (assuming the upper floor functions as the final tread landing), and the pitch angle is derived from the arctangent of actual riser height over tread depth.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Total rise270 cm
- Target riser18 cm
- Tread depth26 cm
Results
- Number of risers15
- Actual riser18 cm
- Total run364 cm
- Angle34.7°
How to use the Stair Calculator
- 1Divide the total vertical rise by the target riser height and round to the nearest whole number to find the number of risers.
- 2Divide the total vertical rise by the rounded number of risers to get the exact actual riser height.
- 3Subtract one from the number of risers and multiply by the tread depth to find the total horizontal run.
- 4Calculate the stair pitch angle by taking the arctangent of (actual riser / tread depth) converted to degrees.
Reading your result
Review the 'Actual riser' and 'Angle' to verify that the staircase falls within comfortable walking limits (often between 30° and 38°) and adheres to local building code limits. The 'Total run' indicates the clear horizontal floor space required on the lower level to accommodate the flight.
Limitations
This calculator models straight-run stairs only and does not account for landings, winders, or stairwell headroom constraints. It also does not factor in tread overhang (nosing) or stringer thickness, which must be detailed during final construction framing.
Common questions
Why is the total run calculated using one less tread than risers?+
In standard stair framing, the upper floor or landing serves as the top tread, meaning a flight with k risers requires k − 1 physical treads along the floor run.
What is considered a safe incline angle for indoor stairs?+
A typical residential stair incline angle sits between 30° and 37°. Angles steeper than 42° can feel excessively steep and may violate local residential building codes.
How does tread nosing affect these calculations?+
Tread nosing (the lip protruding past the riser) increases the effective foot resting surface but does not change the horizontal run between riser faces calculated here.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.