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Vinyl Siding Calculator

Enter your wall perimeter, height and opening area to size your vinyl siding order.

How it is calculated

All lengths are in feet and areas in square feet. The tool works in four steps. Net wall area: net = perimeter × height - openings (never below zero). Add a fixed 10% waste allowance: net × 1.10. Convert to "squares" (1 square = 100 sq ft): squares = net × 1.10 / 100. Finally boxes = ceil(squares / 2), because the tool counts one box as 2 squares (200 sq ft), rounded up to whole boxes.

The starter strip is simply the perimeter, with no extra allowance. The tool assumes a wall that is a plain rectangle: perimeter times a single height, so gable triangles and rooflines must be added to the openings or the height by you. Blank openings count as zero. Trim pieces such as corner posts and J-channel are not calculated, and the 10% waste is fixed, so complex facades may need more.

Worked example

A house has a 160 ft wall perimeter, 9 ft walls and 220 sq ft of windows and doors. Gross wall area is 160 × 9 = 1,440 sq ft. Subtract the openings: 1,440 - 220 = 1,220 sq ft of net area. With 10% waste this becomes 1,220 × 1.10 = 1,342 sq ft, or 13.42 squares. At 2 squares per box, 13.42 / 2 = 6.71, rounded up to 7 boxes. The starter strip is 160 ft, the same as the perimeter.

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Common mistakes

  • Entering the area of the walls as the perimeter. The first field is the distance around the base of the house in feet; the tool multiplies it by the height itself.
  • Typing metres or square metres. Every value must be in feet and square feet, otherwise the order will come out roughly a third of what is needed or vice versa.
  • Forgetting the gables. The height times the perimeter covers only the rectangular walls; triangular gable ends need their own area added to your height or perimeter figures.
  • Entering the window count instead of their combined area in square feet in the openings field.
  • Assuming the box count includes trim. Corner posts, J-channel and soffit are separate and are not counted here.

About this calculator

Vinyl siding is sold by the square — a roofing-and-siding trade unit equal to 100 square feet of coverage — and this calculator counts each box as covering two squares (200 square feet). It takes your wall perimeter and height to find the gross wall area, subtracts the area of doors and windows, adds a fixed 10% waste allowance for cuts, corners, and mismatched panels, and converts the result into squares and boxes plus the starter strip needed to anchor the first course. For a complex facade where you expect more than 10% waste, order an extra box or two.

Homeowners planning a re-siding project and contractors quoting materials use this to avoid two costly mistakes: under-ordering (which risks running out mid-job on a discontinued color or lot) and over-ordering (tying up cash in unused boxes). Getting the waste factor right matters more on complex facades with many corners, gables, and openings than on a simple rectangular wall.

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Comments (1)

  • Editorial team

    The box count assumes a box covers two squares, which is 200 sq ft. Product lines differ, so check the coverage printed on the carton you plan to buy. If it is not 200 sq ft, take the squares figure, which does not depend on box size, and divide it by the squares per carton, then round up yourself. Trim, corner posts and J-channel are separate line items. What box coverage does your siding come with, and which trim pieces do you order?

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