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Siding Calculator

Enter your total wall area, waste percentage and coverage per box.

How it is calculated

All areas are in square feet. The tool first adds the waste allowance: area with waste = wall area × (1 + waste ÷ 100). A square is 100 sq ft, so squares = area with waste ÷ 100. The number of boxes is boxes = ceil(area with waste ÷ coverage per box), always rounded up to a whole box because partial boxes cannot be bought. Wall area and coverage must be above zero; waste can be 0 but not negative. The wall area is taken as given: the tool does not subtract windows, doors or gables, so measure the net area yourself. Use the coverage printed on the product box or spec sheet, in sq ft.

Worked example

A house has 1,800 sq ft of wall to cover, you allow 10% for waste, and each box covers 200 sq ft. Area with waste = 1,800 × 1.10 = 1,980.00 sq ft. Squares = 1,980 ÷ 100 = 19.80 squares. Boxes = 1,980 ÷ 200 = 9.9, rounded up to 10 boxes. The main result is 19.80 squares and 10 boxes. Without any waste allowance the same wall would need exactly 9 boxes, so the 10% allowance adds one box here.

Try this example →

Common mistakes

  • Entering wall area in square metres. The tool works in square feet, so convert first (1 m² is about 10.76 sq ft) and use the box coverage in sq ft too.
  • Confusing a square with one square foot. A square is 100 sq ft; 19.80 squares is nearly 2,000 sq ft, not 19.8.
  • Entering the waste as a decimal (0.1) rather than a percentage. The field expects 10 for 10%; 0.1 would add almost nothing.
  • Forgetting that windows and doors are not subtracted. Enter the gross wall area minus the openings if you want them excluded, and raise the waste for walls with many openings or corners.
  • Using the box coverage in squares, or the coverage of the whole pallet, in place of per-box sq ft coverage. Boxes are rounded up from the figure you give.

About this calculator

Exterior siding is sold and installed by the square — a roofing and siding industry unit equal to 100 square feet of coverage — and packed into boxes that each cover a fixed area, typically listed on the product's spec sheet. Ordering exactly the wall area in siding almost always comes up short once cuts, overlaps, and mistakes are accounted for.

This calculator takes your total wall area, adds a waste percentage (commonly 10–15% for straightforward walls, more for complex cuts around windows and corners), and divides by the coverage per box to tell you how many squares and boxes to buy. Contractors estimating a job and homeowners planning a re-siding project use it to avoid both costly extra delivery trips and over-ordering material that goes to waste.

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Comments (1)

  • Editorial team

    The figure here covers wall panels only. Trim pieces such as corner posts, J-channel, starter strips and soffit are bought by length, not by area, so they need their own count from your wall plan. Siding is also commonly priced per square, which is why the first result is given in squares: it lets you compare supplier quotes directly. Which siding material are you pricing, and what waste percentage did you settle on?

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