What is a square of siding?

One hundred square feet. Siding and roofing are both sold and quoted by the square, and it exists nowhere else in construction — a "square" of drywall or flooring means nothing. A box of vinyl siding usually covers two squares.

Should I deduct windows and doors?

Large ones, yes; small ones, no. The material cut out around a small window mostly becomes offcuts rather than usable pieces, so deducting it makes the order short. The usual rule is to ignore any opening under about 10 square feet and to count a standard door as 21 square feet.

How much waste should I allow?

Ten per cent on a simple rectangular house and fifteen or more where there are dormers, bays or many corners. Every corner is a cut, every cut leaves an offcut, and lap siding cannot be pieced together mid-run where it will be seen.

Does the calculator include trim?

No. Corner posts, J-channel, starter strip and window trim are ordered by the linear foot, not by the square, and their quantity depends on the shape of the house rather than its area. Count corners and openings separately when you order.

Siding Calculator

With perimeter of the house 160 ft, wall height 9 ft, gable ends 2, gable width 30 ft and 6 more fields, siding comes to 17 squares — siding to order. It is reached in 7 steps, the last of which is ceil(1610.4 / 100), and each one is printed on the page with its numbers filled in. The formula is the one published by NIST Handbook 44, Appendix C, not an approximation fitted to it.

Squares of siding for a house from its wall dimensions, with openings deducted and waste added.

Formula and sources checked 27 August 2026 · How we check

Perimeter of the house 160 ft, Wall height 9 ft, Gable ends 2, Gable width 30 ft

17 squares

Siding to order for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.

It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.

Perimeter of the houseAdd the four wall lengths. A 40 by 40 house is 160 ft.Wall heightFloor to soffit. Two storeys at 9 ft is 18.Gable endsTriangles above the wall line. Most houses have two.Gable widthWidth of the wall the gable sits on. Set the gable count to zero for a hipped roof.Gable risePeak height above the wall line.DoorsWindowsAverage window sizesq ftA 3 by 4 window is 12 square feet.Waste allowancepercent10% on a plain house, 15% or more with many corners and cuts.Price per squareusdVinyl runs roughly $200–400 a square in material.

Siding to order

17 squares

Wall area: 160 * 91,440 sq ft
Gable area: 2 * 30 * 7 / 2210 sq ft
Doors and windows to deduct: 2 * 21 + 12 * 12186 sq ft
Area to cover: max(0, 1440 + 210 - 186)1,464 sq ft
With waste: 1464 * (1 + 10 / 100)1,610.4 sq ft
Squares to order: ceil(1610.4 / 100)17 squares
Material cost: 17 * 300$5,100

Several at once

A job is rarely one of anything. Work out the first, add it, change the figures and add the next — the list keeps what each line was, and totals them.

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Worked example

A 40 by 40 single-storey house: 1,440 sq ft of wall plus 210 sq ft of gable, less 186 sq ft of doors and windows, is 1,464 sq ft. With 10% waste that is 1,610 sq ft — 17 squares, since siding is ordered whole.

How to work it out yourself

1.Measure the perimeter at ground level and the wall height to the soffit, not to the roof peak.
2.Add the gables separately: a gable is a triangle, so half its base times its rise.
3.Deduct openings only if they are large. Trade practice is to ignore anything under about 10 square feet, because the offcuts around a small window are rarely reusable.

The formula

Wall area160 * 9
Gable area2 * 30 * 7 / 2
Doors and windows to deduct2 * 21 + 12 * 12
Area to covermax(0, 1440 + 210 - 186)
With waste1464 * (1 + 10 / 100)
Squares to orderceil(1610.4 / 100)
Material cost17 * 300

Source: NIST Handbook 44, Appendix C — general tables of units of measurement

Questions people actually ask

What is a square of siding?: One hundred square feet. Siding and roofing are both sold and quoted by the square, and it exists nowhere else in construction — a "square" of drywall or flooring means nothing. A box of vinyl siding usually covers two squares.
Should I deduct windows and doors?: Large ones, yes; small ones, no. The material cut out around a small window mostly becomes offcuts rather than usable pieces, so deducting it makes the order short. The usual rule is to ignore any opening under about 10 square feet and to count a standard door as 21 square feet.
How much waste should I allow?: Ten per cent on a simple rectangular house and fifteen or more where there are dormers, bays or many corners. Every corner is a cut, every cut leaves an offcut, and lap siding cannot be pieced together mid-run where it will be seen.
Does the calculator include trim?: No. Corner posts, J-channel, starter strip and window trim are ordered by the linear foot, not by the square, and their quantity depends on the shape of the house rather than its area. Count corners and openings separately when you order.

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