Calculate the number of steps, riser height, tread depth, and stringer length. Checks against building code requirements.
Step 1: Measure total rise -- the vertical distance from the finished floor at the bottom to the finished floor at the top.
Step 2: Determine number of risers. Risers = Total rise / Desired riser height. Round to nearest whole number.
Step 3: Calculate actual riser height. Riser height = Total rise / Number of risers
Step 4: Number of treads = Number of risers - 1 (the top floor serves as the last tread).
Step 5: Calculate total run. Total run = Number of treads x Tread depth
Step 6: Calculate stringer length. Stringer = sqrt(Total rise^2 + Total run^2)
Maximum riser height: 7-3/4 inches (196 mm). Many builders prefer 7 to 7-1/2 inches for comfort.
Minimum tread depth: 10 inches (254 mm), measured from nosing to nosing.
Minimum stair width: 36 inches (914 mm) for residential.
Headroom: Minimum 6 ft 8 in (2032 mm) measured vertically from the stair nosing.
Comfort rule: The sum of one riser plus one tread should equal 17 to 18 inches. Riser + Tread = 17-18 in
Riser variation: The difference between the tallest and shortest riser should not exceed 3/8 inch.