Stair Rise and Run Reference

Stairs are the most code-sensitive part of a house. This is the reference for what the code actually says, measured the way an inspector measures it.

Residential stair requirements (IRC)

Item	Requirement
Riser height	7" minimum, 7¾" maximum (7¼" maximum when total rise exceeds 151")
Tread depth	10" minimum, measured nosing to nosing
Riser height variance	No two consecutive risers may differ by more than 3/8" (IRC); 1/4" is a stricter local rule
Headroom	6'-8" minimum along the entire walking line
Width	36" minimum, 44" for a stair serving more than one occupant
Landing	At least as wide as the stair, minimum 36" deep
Total rise between landings	12'-6" maximum without an intermediate landing

Comfortable vs compliant

The code minimums are legal, not comfortable. The " Blondel formula" — riser + tread = 17 to 18 inches — produces stairs that feel right to most adults. A 7 inch riser with an 11 inch tread sums to 18 and feels natural; a 7¾ riser with a 10 inch tread sums to 17.75 and feels steep.

How to measure

Measure risers from the top of the lower tread nosing to the top of each successive tread — not floor to floor. Total rise is the sum of all risers, not the raw floor-to-floor dimension, because the finish floor and the tread thickness occupy part of that gap.

When you must go steeper

Space sometimes forces an unsafe stair. Options that improve it: a landing, a ship ladder (code restricts these), a winder, or moving the stair. What you cannot do is make it steeper and skip the permit — an unpermitted stair is a liability that follows the house.

Where to buy

Compare current pricing across major suppliers — prices vary by region and season.

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