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Generated on: July 20, 2026 at 09:33 PM

Siding Coverage Calculator

Inputs

Wall area140 m²
Openings area14 m²
Waste allowance10 %

Generated with OneCalc · https://onecalc.app/en/construction/siding-coverage

Construction & DIY

Siding Coverage Calculator

Estimate how much exterior siding a project needs. Enter the total wall area, subtract doors and windows, and add a waste allowance to get the coverage in squares, where one square equals 100 square feet.

Inputs

Wall Measurements

%
0 – 100 %

Results

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Siding Needed

\begin{aligned} N &= \dfrac{A_{net}\,(1 + w)}{100\ \text{ft}^2} \\ &= ? \end{aligned}

Details

A_{net} = A_{wall} - A_{open} = 140\,\text{m²} - 14\,\text{m²} = ?\,\text{m²}

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Siding Coverage

Exterior siding is estimated in squares, a trade unit where one square covers 100 sq ft, about 9.29 m²100 sq ft of wall. Turning a set of wall measurements into squares takes three steps: total the wall area, subtract the openings that will not be clad, and add a waste allowance for cutting and trimming.

Net wall area

The starting point is the gross wall area — the height times the width of each wall face, summed across the whole building. Gable ends and other triangular sections count as half of their base times their height.

From the gross area, subtract the openings that carry no siding: doors, windows, and any panelled or masonry sections. What remains is the net area actually covered:

Anet=Awall−Aopen\begin{aligned} A_{net} &= A_{wall} - A_{open} \end{aligned}

Subtracting large openings such as garage doors and picture windows keeps the estimate from ordering material for surfaces that will never be sided. Small windows are sometimes left in, where the offcuts around them would be scrap anyway.

Squares and the waste allowance

Siding is ordered by the square, so the net area is converted from surface area into squares. Because one square covers 100 sq ft, the net area — grown by the waste allowance — is divided by that coverage:

N=Anet×(1+waste)100 ft2\begin{aligned} N &= \frac{A_{net} \times (1 + \text{waste})}{100\ \text{ft}^2} \end{aligned}

The waste allowance covers the pieces cut to length at the end of each course, the trimming around openings, and the occasional broken panel. Around 10% suits long, straight walls. Homes with many corners, gables, or short runs generate more offcuts, so 15% or more is common.

Worked example

A wall with 140 m²1,500 sq ft of gross area, 14 m²150 sq ft of doors and windows, and a 10% waste allowance:

Anet=1500−150=1350 ft2N=1350×1.10100=14.85 squares\begin{aligned} A_{net} &= 1500 - 150 = 1350\ \text{ft}^2 \\ N &= \frac{1350 \times 1.10}{100} \\ &= 14.85\ \text{squares} \end{aligned}

So the job needs about 14.85 squares of siding, which rounds up to 15 squares when ordering full boxes.

Anet=140−14=126 m2N=126×1.109.29 m2=14.92 squares\begin{aligned} A_{net} &= 140 - 14 = 126\ \text{m}^2 \\ N &= \frac{126 \times 1.10}{9.29\ \text{m}^2} \\ &= 14.92\ \text{squares} \end{aligned}

So the job needs about 14.92 squares of siding, which rounds up to 15 squares when ordering full boxes.

Ordering from the estimate

Siding is boxed by the square, and coverage per box varies by profile and by how much overlap each course takes. Round the squares figure up to whole boxes, then keep the waste allowance in mind rather than treating the estimate as an exact cut list. A spare box on hand is usually cheaper than a second delivery partway through the job, and dye-lot differences between orders can be visible on a finished wall.

For the paint or stain that finishes the trim and any painted sections, see the Paint Coverage Calculator.

Frequently Asked Questions (FAQ)

What is a "square" of siding?

A square is the trade unit for exterior cladding and equals 100 square feet of coverage, or about 9.29 square metres. Siding, roofing, and similar materials are quoted and sold by the square, so converting wall area into squares makes it straightforward to order material and compare prices.

How is total wall area measured?

Measure the height and width of each wall, multiply them to get each wall’s area, and add the walls together. Gable ends and other triangular sections are counted as half of their base times height. The sum is the gross wall area entered here before openings are subtracted.

How much waste should be added?

A waste allowance of about 10% is typical for simple, rectangular walls. Homes with many corners, gables, or short runs generate more offcuts, so 15% or more is common there. The allowance covers trimming, breakage, and the pieces left over at the end of each course.

Should doors and windows be deducted?

Large openings such as garage doors and picture windows are worth subtracting because they remove a meaningful amount of coverage. Small windows are sometimes left in as extra waste allowance, since the offcuts around them are rarely reusable. Subtracting openings gives a tighter estimate; leaving them in builds in a margin.

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