Staircase Geometry: Calculating Rise, Run, and Headroom Safety
Stairs are the most dangerous part of a home if built incorrectly. We break down the strict code requirements for Rise (7-3/4 max) and Run (10 min), explain stringer layout, and how to calculate headroom clearance.
Building stairs is a test of precision. Being off by 1/4 inch creates a trip hazard. The human brain memorizes the stair height after the first two steps; if the third step is different, you trip.
The Golden Ratio: 7-11
International Residential Code (IRC) typically mandates:
- Max Riser Height: 7 and 3/4 inches.
- Min Tread Depth (Run): 10 inches.
- Headroom: Minimum 6 feet 8 inches measured vertically from the nosing.
Comfort Rule: Riser + Tread should equal 17-18 inches. A 7-inch rise with an 11-inch run is considered the perfect step.
Calculating the Layout
1. Measure Total Rise: Floor to floor (including finish flooring).
2. Divide by 7: This gives you the approximate number of risers. Round to the nearest whole number.
3. Divide Total Rise by Number of Risers: This gives the exact riser height.
Example: 108 inch total rise. 108 / 15 = 7.2 inches. Perfect.
Try it yourself
Calculate your stair stringer layout:
Remember to account for the thickness of the tread material on the bottom step!