Calculate staircase stringer length, number of risers, exact step rise and run, total horizontal run, incline angle, and IRC building code compliance.
Exact Rise: 7.71" per step
Hypotenuse: 174.4" (14.5 ft)
Amateur builders frequently divide total rise incorrectly, resulting in a bottom step that is 2 inches too short or too tall. The human brain subconsciously remembers step height on the first tread; a variation greater than 3/8 inch causes people to stumble and fall. Our engine calculates uniform riser heights down to the exact fraction.
Failing building inspection halts home construction loans and resale closings. Under IRC Section R311.7, stair risers must never exceed 7.75 inches, treads must measure at least 10 inches deep, and vertical headroom must remain at least 80 inches (6'8"). Our calculator provides immediate pass/fail code diagnostics.
Stair stringers are cut from expensive 2x12 framing timbers. Buying a 10-foot board when the hypotenuse requires 10.4 feet wastes an entire timber. By solving the true Pythagorean hypotenuse and factoring plumb and seat cut margins, our tool recommends the exact nominal lumber board to purchase.
A staircase can meet building code but still feel awkward and exhausting to climb. We calculate Blondel’s classical stride formula ($2 \times \text{Rise} + \text{Tread} = 24\text{–}25\text{ inches}$) and the Rule of 17-18 to ensure natural, effortless walking cadence for children and elderly residents.
| Total Rise (Height) | Number of Risers | Exact Riser Height | Number of Treads | Total Run (10.5" Tread) | Stringer Length | IRC Status |
|---|---|---|---|---|---|---|
| 36.0 inches (Small Deck) | 5 Risers | 7.20 inches | 4 Treads | 42.0 in (3.5 ft) | 55.3 in (8' board) | Compliant (Ideal) |
| 60.0 inches (Porch) | 8 Risers | 7.50 inches | 7 Treads | 73.5 in (6.1 ft) | 94.9 in (10' board) | Compliant (Ideal) |
| 96.0 inches (Basement) | 13 Risers | 7.38 inches | 12 Treads | 126.0 in (10.5 ft) | 158.4 in (14' board) | Compliant |
| 108.0 inches (8' Ceiling) | 14 Risers | 7.71 inches | 13 Treads | 136.5 in (11.4 ft) | 174.1 in (16' board) | Compliant (< 7.75") |
| 120.0 inches (9' Ceiling) | 16 Risers | 7.50 inches | 15 Treads | 157.5 in (13.1 ft) | 198.0 in (18' board) | Compliant |
Measure the plumb vertical distance from finished lower floor to finished upper floor in inches.
Divide total rise by 7.5 target inches to get the exact whole number of uniform risers.
Input horizontal tread depth (min 10.0" per IRC code, typically 10.5" or 11").
Compute horizontal run and solve stringer hypotenuse using the Pythagorean theorem for 2x12 lumber.
Check maximum 7.75" rise limits, Blondel's ergonomic comfort score, and headroom clearance.
Validates against IRC Section R311.7 (maximum 7.75" rise, minimum 10" tread run).
Calculates exact diagonal stringer hypotenuse and recommends standard lumber board lengths (8' to 18').
Evaluates Blondel's historical formula $2R + T = 24\text{–}25"$ and the Rule of 17-18 for comfortable climbing.
Dynamic SVG vector diagram illustrates risers, tread run, stringer cut line, and 80" headroom clearance.
