Stair calculator
Number of steps, riser height, tread depth and stringer length for a staircase.
About this calculator
This stair calculator plans a staircase from the total rise between floors. It gives the number of steps, the exact riser height and the total run.
It also estimates the stringer length and angle, and checks the design against US residential code limits and the comfort rule of thumb.
How it works
The number of risers is the total rise ÷ your target riser height, rounded to a whole number, and the exact riser height is the rise ÷ that number. There is one tread fewer than risers, so the total run is treads × tread depth.
Last reviewed:
Worked example
- Measure in: Inches
- Total rise, floor to floor: 108
- Target riser height: 7.25
- Tread depth: 10.5
Number of risers (steps): 15 (within US residential code limits)
Common questions
How many steps do I need?
Divide the total rise by about 7 inches (18 cm) and round to a whole number. A rise of 108 inches needs 15 risers of 7.2 inches.
What is the maximum riser height?
The US residential code allows up to 7¾ inches (196 mm), with treads at least 10 inches (254 mm) deep. Local codes can differ.
Why is there one tread fewer than risers?
The top step is the upper floor itself, so it needs no tread of its own.
Sources and further reading
The story behind it
Where the idea came from: In the 1670s the French architect François Blondel proposed that two risers plus one tread should equal one stride, about 63 cm.
His rule still guides stair design across Europe. Modern building codes add safety limits, such as a maximum riser height and a minimum tread depth.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
After 15 years as a mathematics educator, I built CalculStore to give students, teachers, professionals and anyone working with numbers simple, reliable tools.
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