Commercial Stair Stringer & Tread Takeoff Calculator
Calculates exact step riser height, tread depth, diagonal stringer length, and number of 2x12 cut stringers required per code based on finished deck or floor-to-floor total rise.
1. Total Vertical Rise & Stair Width
2. Step Riser Height & Tread Run
IRC Stairway Geometry & Dimension Compliance Chart
Authoritative industry reference data complying with IRC Section R311.7 Stairways (Max Riser 7-3/4", Min Tread 10").
| Stair Dimension | Code Requirement (IRC) | Standard Commercial Job Spec | Code Citation |
|---|---|---|---|
| Maximum Riser Height | 7-3/4" (197 mm) | 7-1/4" to 7-1/2" | IRC R311.7.5.1 |
| Minimum Tread Depth | 10" (254 mm) | 11" (2x 5/4x6 boards) | IRC R311.7.5.2 |
| Max Riser Variation | 3/8" (9.5 mm) max delta | < 1/8" delta across flight | IRC R311.7.5.1 |
| Minimum Stair Width | 36" (914 mm) | 36" - 48" clear passage | IRC R311.7.1 |
| Handrail Height | 34" - 38" (864 - 965 mm) | 36" standard graspable rail | IRC R311.7.8.1 |
Transparent Engineering & Takeoff Formulas
Mathematical logic, material density constants, and waste multipliers used in this calculator.
1. Number of Risers
Number_of_Risers = round(Total_Rise_Inches ÷ 7.5)IRC R311.7.5.1 mandates maximum riser height of 7-3/4 inches (197 mm).
2. Exact Unit Riser Height
Unit_Rise = Total_Rise_Inches ÷ Number_of_RisersEqual riser height to eliminate tripping hazards; variation between steps must not exceed 3/8".
3. Number of Treads & Total Run
Number_of_Treads = Number_of_Risers - 1 | Total_Run = Number_of_Treads × Unit_RunTop step lands at upper finished deck/floor level.
4. Stringer 2x12 Board Length
Stringer_Length = √(Total_Rise² + Total_Run²) ÷ 12 + 1 ftDiagonal hypotenuse of stairway plus margin for top plumb cut and bottom level cut.
Frequently Asked Commercial Takeoff Questions
Answering high-intent contractor questions on specifications, sizing, and code requirements.
What is the maximum allowed stair riser height per building code?
Under IRC R311.7.5.1, the maximum riser height is 7-3/4 inches (197 mm), and the minimum tread depth is 10 inches (254 mm) with a 3/4" to 1-1/4" nosing.
How many stair stringers are needed for a deck?
Wood decking planks require stringers spaced at 16 inches on-center max (3 stringers for a 36-inch wide stair). Composite decking (Trex, TimberTech) requires stringers spaced at 12 inches on-center max (4 stringers for a 36-inch wide stair).
What lumber size is used for cut stair stringers?
Building codes require minimum 2x12 #1 or #2 lumber so that at least 3-1/2 inches (5 inches in commercial jurisdictions) of solid throat wood remains after triangular notch cuts.
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