Stair Calculator
Stair layout
Results
| Number of steps | — |
|---|---|
| Riser height | — |
| Tread depth | — |
| Total run | — |
| Stringer length | — |
| 2R + T | — |
How to Use This Stair Calculator
Stair layout is one of those jobs where a half-inch error at the first step becomes a full code violation by the time you reach the landing. I have watched framers cut stringers twice because they divided total rise by tread count instead of riser count, or forgot that the top floor counts as a landing, not a tread. This calculator takes your floor-to-floor height and either a single tread depth or a total horizontal run, then splits the rise evenly across whole steps.
Enter total rise—the vertical distance from finished floor to finished floor—with units in feet, inches, meters, or centimeters. Choose whether you are specifying one tread depth or the total run across all treads. Optionally set a target riser height; the tool divides total rise by that target, rounds up to a whole number of risers, and recalculates the actual riser height so every step is equal.
Results show riser count and tread count, individual riser height, tread depth, total run, stringer length (the hypotenuse along the carriage board), and the comfort check 2R + T—a quick rule carpenters use to see if the stair feels natural underfoot. Ideal comfort lands around 24–25 inches.
Stair Calculator Formulas and Practical Applications
Think of a staircase as a right triangle laid on its side: total rise is the vertical leg, total run is the horizontal leg, and the stringer follows the hypotenuse.
Step 1: Count risers
Number of Risers = Ceiling(Total Rise ÷ Target Riser Height)
Step 2: Actual riser height
Actual Riser = Total Rise ÷ Number of Risers
Step 3: Total run and tread depth
If you enter one tread depth: Total Run = (Risers − 1) × Tread Depth. There is always one fewer tread than risers because the top floor serves as the final step-off.
If you enter total run instead: Tread Depth = Total Run ÷ (Risers − 1)
Step 4: Stringer length
Stringer = √(Total Rise² + Total Run²)
Comfort check: 2R + T ≈ 24–25 in where R is riser height and T is tread depth. A 7.5 in riser with a 10 in tread gives 25 in—right in the sweet spot.
In my experience, a 9 ft floor-to-floor rise with a 7.5 in target riser yields 15 risers at 7.2 in each—a common residential layout that fits most IRC maximum riser heights when verified locally.
Frequently Asked Questions
Why is there one more riser than tread?
The top landing is the final step up—you do not install a tread there. A flight from the first floor to the second with 14 risers has 13 treads between them. Our results label both counts so you can order materials correctly.
What if 2R + T is outside 24–25 inches?
Adjust tread depth or target riser height and recalculate. Stairs that fail the comfort check often feel too steep or too shallow. Also verify riser and tread dimensions against your local building code before cutting stringers.
Does total rise include flooring thickness?
Measure from finished floor to finished floor on both levels. If you are framing before flooring is installed, add the expected finish thickness to your rise measurement or adjust after finishes are spec'd.
Disclaimer. Informational only—not building-code or structural advice. Riser and tread limits vary by jurisdiction (IRC and local amendments); verify with a qualified builder or inspector.