← All tools/Tools/Home & DIY/Stair Calculator
Stair Calculator
Steps, riser height and total run for a staircase from its total rise.
Number of steps
How it works
Steps = total rise ÷ target riser, rounded to the nearest whole step Actual riser = total rise ÷ steps Total run = (steps − 1) × tread depth (the last step lands on the upper floor)
Worked example: a total rise of 300 cm with a target riser of 18 cm gives 300 ÷ 18 = 16.67, rounded to 17 steps. The actual riser is then 300 ÷ 17 = 17.65 cm, and with a 25 cm tread the total run is (17 − 1) × 25 = 400 cm.
Frequently asked questions
Why round the step count?
Because you cannot build a fraction of a step. Rounding gives a whole number of steps, and the actual riser is then adjusted so all steps are equal — equal risers matter far more than hitting the target exactly.
Why is the run (steps − 1) × tread, not steps × tread?
Because the top step is the upper floor itself: you step from the last tread onto the landing, not onto another tread. Counting an extra tread would overstate the run by one tread depth.
What is a comfortable riser height?
Around 17 to 19 cm with a tread of 25 to 28 cm suits most homes. Local building rules may set limits, so check them before building — this calculator does the geometry, not the regulations.
More tools
Tell us what you think
Loving this tool, or stuck on something? Tell us — it takes a minute.
We’ll only use your name and email to reply if needed. The tool and page are filled in for you.