🪜 Stair Calculator
Plan a staircase by entering the total height and run available — get the number of steps, rise and run per step, and stringer length.
How the Stair Calculator Works
The calculator divides the total floor-to-floor height by your maximum allowed riser height and rounds up to find the minimum number of steps needed, then divides the total rise evenly across those steps to get the actual riser height — this keeps every step the same, which is important for safety and often required by building code.
Run and Stringer Length
Using your chosen tread depth, the calculator multiplies it by the number of treads (one fewer than the number of risers, since the top step is usually the upper floor itself) to find the total horizontal run required. The stringer length — the diagonal board that supports the steps — is then found with the Pythagorean theorem from the total rise and total run.
Common Guidelines
- Most residential building codes call for a maximum riser height around 7.75 inches and a minimum tread depth around 10 inches, though local codes vary and should always be checked.
- Keeping riser heights consistent within about 3/8 inch across a staircase is a standard safety practice to prevent trips.
- This calculator estimates dimensions for planning purposes; final stair construction should follow your local building code and, where required, a licensed professional’s review.
Provided for general planning and educational purposes only.