Stair Rise and Run: The Math Behind a Comfortable Staircase

"Rise" is the height of each step, "run" is its depth, and codes set both a minimum and maximum for each because a stair that's too steep is a fall risk and one that's too shallow forces an awkward, unnatural stride. There's also a consistency requirement: every step in a single flight has to be close to the same height, since an uneven stair is one of the more common causes of a missed step and a fall.

Residential stairs typically allow a steeper, more compact ratio than stairs in a public building, reflecting the difference between a stair used occasionally by familiar occupants and one used constantly by strangers. If a set of stairs you're building feels wrong on paper, it's worth double-checking the rise and run against the range for the occupancy type before you cut a single stringer.