How do you calculate the length of a stair stringer board?

Stringer Board Length = √(Total Run² + Total Rise²), rounded up to the nearest standard lumber size (e.g. 2x12 in 10ft, 12ft, or 14ft lengths).

Stairs & StringersConstruction

Stair Riser, Tread, Stringer Length & Blondel's Rule Calculator

Calculate exact stair riser heights, tread run depths, total step count, stringer cut lengths, and stair incline angle conforming to building codes and Blondel's formula.

Construction & Building Civil & Structural Engineering DIY & Home Improvement

Calculated Result

Exact Calculated Riser Height (cm)

17.5cm

Calculator Inputs

Total Floor-to-Floor Stair Rise (cm)

Quick select:

Target Riser Height (Ideal ~17.5 cm)

Quick select:

Desired Tread Depth (Ideal ~28-30 cm)

Quick select:

Exact Calculated Riser Height (cm)

17.5cm

Total Number of Risers

16 risers

Total Number of Treads

15 treads

Stair Stringer Length (m)

5.05 m

Stair Incline Slope Angle (°)

33.7 °

Total Horizontal Run on Floor

4.2 m

Blondel Ergonomic Score (2R + T)

63 cm

Total Rise vs. Total Run vs. Stringer Length Breakdown

Total Horizontal Run on Floor

4.2 m(35%)

total_rise_m

2.8(23%)

Stair Stringer Length (m)

5.05 m(42%)

Standard residential building codes specify maximum 7.75" (19.7cm) riser height and minimum 10" (25.4cm) tread depth.

All engineering calculations, structural estimates, and electrical sizing metrics are provided for preliminary estimation only. Always ensure compliance with relevant statutory building codes and occupational safety standards, verified by a certified professional engineer before practical implementation.

Calculation Methodology

Number of Risers = Round(Total Rise / Target Riser 17.5cm). Exact Riser = Total Rise / Number of Risers. Number of Treads = Number of Risers - 1. Total Run = Treads * Tread Depth.