Siding Guide: Everything You Need to Estimate
To estimate siding, find the wall area (perimeter × height), add 10–15% for waste, then divide by 100 for squares. Multiply the area by the installed price per square foot — vinyl runs about $4–$8 and fiber-cement $6–$13. A 40×30 ft home with 9 ft walls needs about 1,386 ft² of siding.
Get exact numbers
Use the free Siding Calculator to estimate your project.
How to estimate siding
Formula: Siding (ft²) = Perimeter × Height × (1 + waste %); Squares = area ÷ 100
- Measure the perimeter. Add the length of all exterior walls (2 × (length + width) for a rectangle).
- Multiply by wall height. This gives the gross wall area in square feet.
- Add waste. Add 10% for simple walls, 15% for homes with many corners and openings.
- Convert to squares. Divide by 100. Siding is ordered and priced by the square.
Example: A 40 ft × 30 ft home with 9 ft walls: perimeter 140 ft × 9 = 1,260 ft² × 1.10 ≈ 1,386 ft² (≈ 13.9 squares).
Common mistakes to avoid
Not subtracting large openings
Big windows, garage doors, and entries reduce the siding area — but keep the waste factor for cuts around them.
Forgetting trim and accessories
J-channel, corner posts, starter strip, and house wrap add to the order and the budget.
Skipping house wrap
A weather-resistant barrier behind the siding prevents moisture damage and drafts.
Underestimating gables
Triangular gable walls add area that a simple perimeter × height misses — measure them separately.