Staircase Calculator (Number of Steps and Tread Depth)
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
The number of steps is calculated by dividing the total height to climb by the desired step height, rounded to the nearest whole number. For a height of 260 cm with 18 cm steps, you need 14 steps, each actually measuring 18.57 cm.
Explanation
Designing a comfortable staircase requires adjusting two dimensions together: step height (or riser) and tread depth (where you place your foot). This calculator starts by determining the whole number of steps needed to climb the total height with a step height close to the desired one, then recalculates the actual step height once that number is rounded (it differs slightly from the desired value, barring an exact coincidence). It then applies Blondel's formula, an empirical comfort rule widely used in France since the 17th century: the sum of twice the step height and the tread depth should be close to an adult's natural stride, about 63 cm (2h + g ≈ 63, with an acceptable range of 58 to 66 cm for a private home, narrowed to 60-64 cm in buildings open to the public). A taller step therefore needs a narrower tread, and vice versa, to stay comfortable to climb. The French standard NF P01-012 further specifies independent minimum values: a tread depth of at least 25 cm and a step height generally between 17 and 18 cm for everyday use.
Example: climbing 260 cm with 18 cm steps
Inputs
Total height: 260 cm. Desired step height: 18 cm.
Calculation
Number of steps = round(260 ÷ 18) = round(14.44) = 14. Actual step height = 260 ÷ 14 ≈ 18.57 cm. Blondel tread depth = 63 − 2 × 18.57 ≈ 25.86 cm.
Result
You need 14 steps, each 18.57 cm tall, with a comfortable tread depth of about 25.86 cm under Blondel's formula.
Frequently asked questions
Why does the actual step height differ from what I entered?
Because the number of steps has to be a whole number: the total height is therefore spread across that whole number of steps, giving a height slightly different from the value you started with, unless the division comes out even. It's this actual height, not the desired value, that should be used to build the staircase.
What if Blondel's recommended tread depth is too narrow or too wide for my space?
Blondel's tread depth is a comfort recommendation, not a universal building requirement. If the available space calls for a different tread depth, it's still possible to deviate from this value, keeping in mind that a too-steep staircase (tall steps, narrow tread) will be more tiring and less safe, while a too-shallow one will take up more floor length for the same height.
Is Blondel's formula a mandatory standard in France?
No, it's an empirical comfort rule, widely followed but not required by regulation in private homes. Buildings open to the public, however, are subject to stricter rules (the NF P01-012 standard, a narrower 60 to 64 cm range), notably for accessibility and safety.