Stair Calculator
Calculate the number of steps, riser height and tread depth for any staircase.
This free stair calculator helps you plan a comfortable, code-compliant staircase. Enter the total rise (floor-to-floor height) and the total run (horizontal length available), and the calculator works out how many steps fit, the exact riser height and tread depth for each step, and checks the result against the widely used comfort rule that riser + tread should fall between roughly 43 and 48 cm (17–18 in).
Getting riser and tread dimensions right matters for safety and comfort: risers that are too tall or treads that are too shallow make a staircase tiring and increase the risk of trips, while consistent, well-proportioned steps feel natural to walk on. Always check your local building code, since exact minimum and maximum values vary by country.
Frequently Asked Questions
What is stair "rise" and "run"?
Total rise is the vertical floor-to-floor height the staircase needs to climb. Total run is the horizontal distance available for the staircase to travel while climbing that height.
What is a riser and a tread?
The riser is the vertical face of a single step (its height), and the tread is the horizontal surface you step on (its depth). Together, riser and tread height determine how steep or gentle a staircase feels.
How do I calculate the number of steps?
Divide the total rise by a target riser height (commonly 17–18 cm) and round to the nearest whole number. This calculator does that automatically and then recalculates the exact riser height so all steps are equal.
What is the 2R + T comfort rule?
A widely used rule of thumb states that twice the riser height plus the tread depth (2R + T) should fall between about 63 and 65 cm for a comfortable stride. This calculator checks your result against that range.
What is a comfortable riser height?
Most residential building codes recommend a riser height between about 15 and 18.5 cm (6–7.3 in). Lower risers feel gentler but require more horizontal space.
What is a comfortable tread depth?
A tread depth of at least 25–28 cm (10–11 in) is generally recommended so a normal-sized foot fits comfortably on each step.
Why must all steps have the same height?
Uneven riser heights within the same staircase are a leading cause of trips and falls, because people unconsciously expect every step to be the same height once they start climbing.
Does this calculator account for building codes?
It applies the widely used comfort formula and general residential guidelines, but exact legal minimums and maximums vary by country and building type — always confirm with your local building code before construction.
Can I use this for outdoor stairs?
Yes, the same rise/run math applies, though outdoor stairs are often built with slightly shallower risers and deeper treads for extra safety in wet or icy conditions.
What if my total rise doesn't divide evenly?
The calculator rounds to the nearest whole number of steps and then recalculates the exact riser height needed, so the final riser may differ slightly from your original target — this is normal and expected.