Siding Calculator
Siding Coverage Starts with What You're Not Covering
The gross wall area of a house includes every window, door, and vent opening that siding will never actually touch. Subtracting those openings before ordering material is what keeps a siding estimate from running well over what the job actually needs.
The Formula
Net Area = Gross Area − Openings Area
Siding Needed = Net Area × (1 + Waste%)
The calculator multiplies total wall length by height to get the gross area, subtracts the combined area of doors, windows, and other openings, and then applies a waste allowance — 10% by default — to cover cutting, overlap between courses, and pattern-matching losses at corners. In feet, it also converts the result into siding "squares," the trade unit equal to 100 sq ft.
Where This Calculation Matters
- Full house re-siding — siding is sold by the square, so converting a net wall area into squares is what lets you compare pricing and place an order with a supplier.
- Additions and single-wall repairs — matching an existing siding profile on a smaller wall still needs the same opening deductions to avoid over-ordering.
- Lap and panel siding overlap — horizontal lap siding courses overlap each other, which is part of what the waste allowance is meant to absorb beyond simple cutting losses.
Worked Example
A 40 ft × 9 ft wall (360 sq ft) with 40 sq ft of door and window openings:
| Step | Calculation | Result |
|---|---|---|
| Gross wall area | 40 × 9 | 360 sq ft |
| Net area | 360 − 40 | 320 sq ft |
| Siding needed (incl. 10% waste) | 320 × 1.10 | 352 sq ft |
| In squares | 352 ÷ 100 | 3.52 squares |
How to Use This Calculator
- Select Feet or Meters.
- Enter the wall's Length and Height.
- Enter the Openings Area for doors and windows to subtract.
- Optionally adjust the Waste % — defaults to 10%.
- Select Calculate to see the siding needed in area (and squares, if using feet).
Related Calculations
Insulating before the siding goes on? The Insulation Calculator covers the wall cavity, and the Paint Calculator handles interior walls using a similar opening-deduction approach.