How to calculate siding
Siding is estimated from the net wall area, then converted to squares:
Wall area = perimeter × height − openings, then squares = area × (1 + waste) ÷ 100
The perimeter is the sum of all the walls you're siding; multiply by the average wall height for gross area, then subtract roughly 21 sq ft per door and 15 per window. Add a waste allowance for cuts around corners and openings, divide by 100 to get squares, and round up. Triangular gable ends should be added on top (base × height ÷ 2 each).
Siding by the numbers
| Unit | Covers |
|---|---|
| 1 square | 100 sq ft of wall |
| 1 box of vinyl (typical) | 2 squares / 200 sq ft |
| Simple boxy house | ~10% waste |
| Many corners & gables | ~15%+ waste |
Good to know
- Don't forget trim. J-channel, corner posts, starter strip, and soffit are bought separately from the field siding.
- Gables add up. Each triangular gable is base × height ÷ 2 — add them to your wall area.
- Order one dye lot. Buy all the siding together so the color matches across boxes.
- This is a material estimate. It doesn't include house wrap, insulation, or labor.