Free estimate — verify against local code before building
Siding Calculator
Siding squares, cartons or pieces, housewrap, trim, fasteners, and cost.
What this calculator includes
Enter a representative rectangular wall and the number of similar walls, then add triangular gables and subtract windows, doors, or other openings. Choose vinyl, fiber-cement lap, or panelized board-and-batten planning mode. The calculator shows net siding area, waste, squares, cartons or pieces, editable product coverage and cost, plus housewrap, starter, channel, corners, fasteners, flashing, sealant, and trim. Every assumption remains visible because actual coverage and installation requirements vary by product.
How to use this siding calculator
- 01
Measure rectangular walls
Measure wall length and height, then enter how many walls use that size. Run separate estimates for substantially different wall sizes and add the order quantities.
- 02
Add triangular gables
Measure each gable's base and vertical height from the wall plate to the peak. The calculator uses base × height ÷ 2 and multiplies by the gable count.
- 03
Subtract openings
Enter window and door counts with average dimensions, plus any other combined opening area. Opening perimeter also sizes flashing and, for vinyl, J-channel.
- 04
Verify product coverage
Select a planning mode, then replace the example coverage and price with the exact carton, board, or panel label. Coverage after laps and overlaps—not nominal size—controls the order.
Calculation sources and review
Primary references and formula assumptions are linked so you can verify them against the selected product, supplier, and adopted local requirements.
Internal formula review completed July 13, 2026. What this review covers
- Vinyl Siding Institute — Installation Manual (opens in a new tab)
Installation, flashing, clearance, and fastening guidance for vinyl siding.
- James Hardie — Installation Instructions (opens in a new tab)
Manufacturer instructions used as a cross-check for fiber-cement planning assumptions.
- EPA — Lead Renovation, Repair and Painting Program (opens in a new tab)
Safety context for work that disturbs painted surfaces in pre-1978 buildings.
Frequently asked questions
How many square feet are in a square of siding?
One siding square equals 100 square feet of installed wall coverage. Product cartons and boards may cover a fraction or multiple of a square, so use the coverage printed on the package.
How much extra siding should I order?
Ten percent is a common starting point for simple vinyl elevations. Use 12–15% for fiber-cement, many corners, short wall sections, detailed gables, or layouts that create more offcuts.
Should I subtract windows and doors from siding area?
Yes for quantity planning, especially on elevations with large openings. Waste often absorbs very small openings, but entering them explicitly also produces a better flashing, J-channel, and trim estimate.
Does siding need housewrap?
Most assemblies require a code-compliant water-resistive barrier behind siding, integrated with window, door, and penetration flashing. Requirements depend on the wall assembly, local code, and manufacturer's instructions.
Can I use nominal board dimensions as installed coverage?
No. Lap siding loses width to exposure overlap, vinyl coverage varies by profile and carton, and board-and-batten systems vary by seam or batten detail. Always enter the manufacturer's stated installed coverage.