How to use the Stair Calculator
Start with the height between finished floors, the riser height you want to approach, and the depth of each tread. The Stair Calculator converts the entries to inches, chooses a whole number of risers, and shows the resulting riser height, tread count, total run, stringer length, and stair angle. It keeps the entered values, converted rise, raw riser count, formula, and 2R + T check in the result.
Enter measurements in the Stair Calculator
- 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 accepts inches, feet, centimeters, or meters.
- Select Calculate. Select Reset to restore 108 in, 7 in, and 10 in with inch units.
Total rise accepts 0.01 through 600 in the unit selected for that field. Target riser height accepts 1 through 12, and Tread depth accepts 4 through 24, also in the selected unit. A blank, non-numeric, or out-of-range entry shows an error. The converted Target riser height must be smaller than the converted Total rise.
How the stair riser and tread calculation works
All three measurements are converted to inches first. The calculator divides Total rise by Target riser height and rounds the result to a whole number of risers. It then divides Total rise by that count, so every riser uses the same Actual riser height. Number of treads equals Number of risers minus one, and Total run equals Number of treads multiplied by Tread depth.
Input: 108 in rise, 7 in target riser, 10 in tread
Output: 15 risers, 7.2 in actual riser, 14 treads
Total run: 140 in | Stringer: 14.735 ft | Angle: 37.65°Stringer (sloped) length uses sqrt(Total rise^2 + Total run^2). Stair angle uses atan(Total rise / Total run) and is measured from horizontal. The result table keeps the raw riser count beside the rounded count, so you can see how the requested height led to the chosen number of risers.
What the Stair Calculator reports
The result shows Number of risers, Actual riser height, Number of treads, Stair angle (from horizontal), and Stringer (sloped) length. Its table also includes the entered Total rise, the rise converted to inches, the entered Target riser height and Tread depth, Total run, the raw riser count, and the intermediate values used in the formulas.
The 2R + T check adds twice the Actual riser height to Tread depth. A value from 24 through 25.25 inches receives the label within this calculator's reference range. The calculation does not inspect riser limits, tread limits, headroom, landings, nosing overhangs, or other local requirements.
Where stair calculations come up
Enter the floor-to-floor measurement before sketching a straight stair flight. Number of risers and Total run give the vertical and horizontal dimensions used in that layout.
When a tread depth is fixed, change Target riser height and compare the raw and rounded riser counts with the resulting Actual riser height.
After calculating, select Copy result to place the plain-text output on the clipboard. Select Download result (.txt) to save the same result as a text file.
When another construction calculator fits better
Use the Stair Calculator for a straight flight with equal risers and equal treads. For other dimensions and material quantities, browse Construction Calculators. Choose the Ramp Calculator for rise, run, slope grade, angle, or landings. Choose the Roof Pitch Calculator for roof rise, run, pitch angle, and rafter length. Choose the Construction Materials Calculator for one of its 23 project modes, including stairs.
Frequently asked questions
How does the stair calculator determine riser height?
It rounds Total rise divided by Target riser height to a whole number of risers, then divides Total rise by that count to get the actual riser height used for every riser.
How do I calculate stair tread depth and total run?
Enter Tread depth, and the calculator multiplies it by Number of treads, where Number of treads equals Number of risers minus one. The result is Total run, shown in feet and inches.
How is stair angle calculated?
Stair angle is calculated with atan(Total rise / Total run) and displayed in degrees from horizontal. When total run is zero, the calculator reports 90 degrees.
Can this stair calculator check building-code requirements?
This calculator reports stair geometry from the three entered measurements. Building-code compliance depends on local requirements and the use case. The calculation does not inspect landings, headroom, nosing overhangs, or local maximum and minimum requirements.
Can I use feet or centimeters in the stair calculator?
Yes. Total rise, Target riser height, and Tread depth each accept inches, feet, centimeters, or meters, and each unit can be selected independently.