How to calculate stairs
Measure the total rise from finished floor to finished floor. Divide it by the maximum riser height you want and round up: that is the number of steps. The real riser height is the total rise divided by that number, so every step is exactly the same.
The comfort rule
A staircase feels natural when two risers plus one tread equal a normal stride of about 600–650 mm (24–25 in). This rule from the 17th century, called the Blondel formula, still appears in building guidelines.
Building codes
US residential code (IRC) allows risers up to 7¾ in with treads of at least 10 in. In the UK the maximum rise for a private stair is 220 mm, and many European countries set similar limits. Always check your local code before building.