Stair Calculator
Enter the total rise from floor to floor, the riser height you would like and the tread depth to see the number of steps, the exact riser height, the total run, the stringer length and the angle.
How to use this stair calculator
- Measure the total rise from the finished bottom floor to the finished top floor. This is the vertical distance, not the length of the stairs.
- Enter the riser height you would like. Many homes use around 7 inches, but follow your local code.
- Enter the tread depth. This is the horizontal depth you want for each step.
- Press Calculate to see the number of risers, the exact equal riser height, the total run, the stringer length and the angle.
- Use Copy result or Export CSV to give the numbers to your builder or to mark out your stringers.
How to calculate stair rise, run and stringer length
Stairs are a series of equal right triangles. The calculator splits the total rise into whole, equal risers.
- Number of risers = total rise / desired riser height, rounded to a whole number
- Exact riser height = total rise / number of risers
- Number of treads = number of risers – 1, because the upper floor acts as the last tread
- Total run = number of treads x tread depth
- Stringer length = square root of (total rise squared + total run squared)
- Angle = arctan(total rise / total run)
A common comfort check is riser x 2 + tread, which designers often aim to keep near a typical stride. The result is shown so you can compare it with your own target.
Worked example
The total rise is 105 inches and you would like 7 inch risers. 105 / 7 = 15, so you need 15 risers and each one is exactly 7 inches. There are 14 treads. With 10 inch treads the total run is 14 x 10 = 140 inches, or 11.67 feet. The stringer length is the square root of (105 x 105 + 140 x 140) = the square root of 30,625 = 175 inches, or 14.58 feet. The angle is arctan(105 / 140) = 36.9 degrees.
Riser x 2 + tread = 2 x 7 + 10 = 24 inches.
Assumptions & limits
- All risers are equal and all treads are equal. Winders, landings and spiral stairs are not covered.
- The stringer length is the straight line from bottom to top. A real stringer needs extra length for cuts, bearing and the sizes of the lumber.
- Tread depth is the run of each step. Nosing, if any, is separate and depends on the stair design.
- Building codes set limits on riser height, tread depth and headroom. They differ by place and by use, so check your local code before building. This tool does not tell you whether a design is legal.
- Measure the rise carefully, because a small error repeats on every step.
Frequently asked questions
How do I calculate the number of stairs?
Divide the total rise by the riser height you want and round to a whole number. A rise of 105 inches with 7 inch risers gives 15 risers. The upper floor counts as the last tread, so there are 14 treads.
What is a good riser height and tread depth?
It depends on the building and the local code. Many homes use risers near 7 inches and treads of 10 inches or more, but check the rules where you live.
How do I find the stringer length?
Use the Pythagorean theorem on the total rise and total run. The stringer length is the square root of rise squared plus run squared.
Why is there one fewer tread than risers?
The top floor takes the place of the last tread, so a staircase with 15 risers has 14 treads.
What is total run?
It is the horizontal distance the stairs cover, which is the number of treads times the tread depth.
Does this meet building code?
The calculator does not check code. Compare the result with the rules for your area and ask your building department if you are not sure.
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Last updated: November 2026