Siding Overlap and Exposure Calculator
Calculate the exposure (face width), overlap, number of courses, and total siding needed for your siding project.
Formulas Used
Exposure = Panel Width − Overlap
Number of Courses = ⌈ Wall Height ÷ Exposure ⌉ (ceiling / round up)
Linear Feet (no waste) = (Courses × Wall Width) ÷ 12
Linear Feet (with waste) = Linear Feet (no waste) × (1 + Waste% ÷ 100)
Total Board Area = Linear Feet (with waste) × (Panel Width ÷ 12)
Assumptions & References
- All inputs are in inches; area results are in square feet and length in linear feet.
- Overlap (lap) is the portion of each board hidden behind the board above it. Typical lap is 1"–1.5" for most horizontal siding.
- Exposure is the visible face of each installed board: Exposure = Panel Width − Overlap.
- Courses are always rounded up to ensure full wall coverage.
- A waste factor of 10% is standard for straight runs; increase to 15–20% for complex cuts, angles, or windows.
- This calculator covers a single rectangular wall section. Subtract window and door openings separately, then apply waste.
- Minimum overlap per most building codes and manufacturer specs is 1 inch for weather resistance (IRC R703).
- Reference: International Residential Code (IRC) Section R703 – Exterior Covering; manufacturer installation guides (e.g., James Hardie, LP SmartSide).