Use our free Stair Calculator to size risers, determine treads, check the 2R+T comfort rule, and estimate stringer length for safe, code-conscious stair design.
What the Stair Calculator Does
Designing stairs is part geometry, part comfort science. Enter your total rise (floor-to-floor height), preferred riser height, and tread depth. The Stair Calculator finds the nearest whole number of risers, adjusts the actual riser height so the stairs meet your exact total rise, calculates number of treads, total run, stair angle, and stringer length. You can also include nosing (overhang) and stair width to get a stringer count suggestion.
Key Outputs You’ll Get
- Number of risers and adjusted riser height
- Number of treads and total run
- Stringer (hypotenuse) length
- Stair angle (pitch) in degrees
- 2R+T comfort check for walkability
- Recommended number of stringers based on stair width
How to Use the Stair Calculator
- Select your unit system: inches (Imperial) or millimeters (Metric).
- Enter Total Rise: measure from finished lower floor to finished upper floor.
- Enter Desired Riser Height: typical residential target is 7 to 7.75 inches (175–200 mm).
- Enter Desired Tread Depth (going): commonly 10–11 inches (250–280 mm).
- Optionally add nosing/overhang and stair width for more detailed results.
- Choose whether to count the top floor as a tread (affects tread count and run).
- Click Calculate to get your results instantly.
Understanding Stair Math
The calculator rounds the riser count to a whole number, then re-distributes the total rise to produce an even riser height across the flight. Tread count is usually one less than riser count when the upper floor acts as the final riser; if you “include top tread,” the tread count matches the riser count. Total run equals tread count multiplied by the chosen tread depth (the horizontal going per step).
Stringer length is the hypotenuse of a right triangle formed by the total rise and total run. The stair angle is arctangent of rise/run. For comfortable walking, many builders use the 2R+T rule: two times the riser height plus the tread depth should be around 24–25 inches (about 600–635 mm).
Code, Comfort, and Safety
Building codes vary by location. Common guidelines include maximum riser height and minimum tread depth, consistent riser heights within the same flight, and acceptable stair angles. Always check local code before cutting lumber. The Stair Calculator helps you refine a design that’s in the right ballpark for both comfort and compliance.
Tips for Accurate Measurements
- Measure finished floor to finished floor, including flooring thicknesses.
- Account for nosing if your tread depth includes an overhang.
- Plan for consistent risers: the calculator evens them automatically.
- For wider stairs, consider more stringers to reduce tread flex.
From Layout to Cut List
With rise and run in hand, you can lay out the step triangles on a stringer using a framing square, marking each rise and run, then cutting along the lines. The calculator’s outputs make it easy to produce a quick cut list, estimate material length, and preview the finished angle before you build.
Who Is This For?
DIYers, contractors, architects, and anyone who needs accurate stair dimensions. Whether you’re planning interior stairs, a deck staircase, or replacing an old flight, the Stair Calculator gives you reliable numbers fast.
Get Started
Enter your dimensions in the form above and press Calculate. In moments, you’ll have the number of steps, total run, angle, and stringer length—plus a comfort check using 2R+T. Use the results to guide your layout and confirm your design is safe and comfortable.