Stair calculator (steps, riser height)
Calculate the number of steps, the exact riser height and a comfortable going (tread depth) for a staircase, based on the total height to climb. The calculation follows Blondel's formula, used in architecture, and stays entirely local.
How it works
Designing a comfortable staircase takes more than dividing the total height by an arbitrary number of steps: the height of each step (the "riser") and its depth (the "going") must stay in proportions that match the natural length of a human stride. Enter the total height to climb (for example the floor-to-ceiling height between two stories) and a comfortable target riser height, and the tool adjusts the number of steps to get an even actual riser height.
What is Blondel's formula?
Blondel's formula (2 × riser height + going ≈ 63 cm, sometimes between 60 and 64 cm) is a 17th-century rule of thumb still used in architecture to size a staircase that is comfortable to climb and descend. It assumes that a natural stride measures about 63 cm on the ground, and that a step should reproduce that same amplitude by combining rise and run.
Why does the actual riser height differ from my target value?
The number of steps must be a whole number: the tool therefore rounds the number of steps to the nearest integer, then recalculates the exact height of each step by dividing the total height by that whole number. The result is very close to your target value, but rarely identical to the millimeter.
This geometric calculation runs entirely in your browser, with no data sent to a server.