What This Tool Calculates
Enter a total rise, target riser height, and tread depth. The calculator estimates the riser count, actual riser height, tread count, total run, stringer length, stair angle, and a 2R + T reference classification. These are mathematical estimates, not construction or code-compliance decisions.
Enter the Stair Measurements
- Enter the Total rise (floor-to-floor height).
- Enter the Target riser height.
- Enter the Tread depth.
- Choose a unit for each field. Each selector supports inches, feet, centimeters, and meters independently.
- Select Calculate. Use Reset to restore the starting values.
The accepted ranges are 0.01–600 for total rise, 1–12 for target riser height, and 4–24 for tread depth, all in the entered unit. The target riser must also be smaller than the total rise.
Read the Calculated Result
The result shows headline values for risers, actual riser height, treads, stair angle, and stringer length. Its table includes selected converted and calculated values, the raw and rounded riser count, total run, and the 2R + T check. Numeric results use fixed decimal formatting; the raw riser count is also reported. The headline stringer length is in feet, with inches included in the table.
The 2R + T value is calculated as 2 x Actual riser height + Tread depth. The tool classifies 24 through 25.25 inches as within its reference range. This is informational only.
Calculation Logic
Number of risers = round(Total rise / Target riser height)Actual riser height = Total rise / Number of risersNumber of treads = Number of risers - 1Total run = Number of treads x Tread depthStringer length = sqrt(Total rise^2 + Total run^2)Stair angle = atan(Total rise / Total run)
The riser count is rounded to the nearest whole number and clamped to at least one. For example, 108 in rise, 7 in target riser, and 10 in tread depth gives 15 risers, a 7.2 in actual riser, 14 treads, and 140 in total run.
Use the Result Controls
Select Copy result to copy the generated plain-text summary. Select Download result (.txt) to save that summary as a text file.
Limitations and Edge Cases
- The model covers one straight flight with equal risers and equal treads.
- It does not look up building codes or model landings, winders, headroom, or nosing overhangs.
- Rounding can produce one riser and zero treads for some inputs. With zero total run, the calculated angle is 90 degrees.
- The output is a geometry estimate. It does not validate construction suitability or jurisdiction-specific requirements.
Privacy Scope
The stair calculation runs in the page interface using the values entered into the calculator. This page also loads analytics scripts, and its separate subscription form sends an entered email to /assets/subscribe.php. The local implementation does not support a broader claim that all page data stays local or is never sent to a server.
Frequently Asked Questions
What is the stair riser and tread formula?
Number of risers = round(Total rise / Target riser height). Actual riser height = Total rise / Number of risers. Number of treads = Number of risers - 1. Total run = Number of treads x Tread depth. Stringer (sloped) length = sqrt(Total rise^2 + Total run^2). Stair angle = atan(Total rise / Total run). For example, a 108 in total rise with a 7 in target riser and a 10 in tread gives 15 risers, an actual riser height of 7.2 in, 14 treads, a 140 in total run, and a stair angle of about 37.6 degrees.
Why does the calculator adjust my riser height?
You cannot always divide the total rise evenly by your target riser height. The calculator rounds to the nearest whole number of risers, then divides the total rise by that whole number to get the actual riser height every step will use, so all risers in the flight are equal.
What is the 2R + T comfort check?
Twice the riser height plus the tread depth (2R + T) is a commonly used stair-geometry reference. This calculator classifies values from 24 through 25.25 inches as within its reference range. It is not a building-code requirement and does not override your local code.
Does this tool guarantee my stairs meet building-code requirements?
No. It performs a transparent geometry calculation using only the total rise, target riser height, and tread depth you enter. Maximum riser height, minimum tread depth, headroom, and other requirements vary by jurisdiction and use case - confirm requirements with your local building code and a qualified professional before building.
What units are supported?
Total rise, target riser height, and tread depth each accept inches, feet, centimeters, or meters, chosen independently for each field.