Rise = the vertical height of each step. Run = the horizontal depth. Building codes regulate both for safety.
IRC Building Code (Residential)
- Maximum rise: 7.75 inches (197 mm)
- Minimum run: 10 inches (254 mm)
- Minimum headroom: 6 ft 8 in
- Minimum width: 36 inches
Comfort Formula
2 × rise + run = 24–25 inches (ideal). At 7" rise and 11" run: 2(7)+11 = 25" — perfect.
Total Steps
Number of steps = Total floor-to-floor height ÷ individual rise height.
Why the 2×Rise + Run Rule Exists
This formula (sometimes stated as 24–25 inches, sometimes 17–18 for rise+run alone) approximates the natural stride length of an average adult walking up and down stairs — stairs built outside this range feel awkward or unsafe even if every individual step meets minimum code, because the rhythm of walking doesn't match the step spacing.
Consistency Matters More Than the Exact Number
Building code is actually stricter about consistency between steps than about the exact rise/run values — a variance of more than 3/8" between the tallest and shortest riser in the same staircase is a leading cause of trip-and-fall accidents, since the body unconsciously expects every step to match the first one climbed.