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Siding Calculator: How Much Siding Do I Need?

Work out how many squares of siding a house needs from its walls and gables, minus windows and doors, with trim, waste and cost. Measure the house or list the walls, choose vinyl boxes or lap planks, and use the result for the order or the quote.

Your numbers

House

ft
ft
ft

Gables

ft
ft

Each gable is a triangle: base × height ÷ 2. Use 0 for a hip roof.

Windows and doors

in
in
in
in

Siding

sq ft

Most vinyl comes 2 squares (200 sq ft) to a carton; check the label.

%

Typical 10 % for cuts, gables and corners. Added to siding and trim.

Trim

ft
ft
ft

The two sloped edges of each gable.

Piece lengths are typical; edit them to your product.

Soffit and fascia (optional)

ft
in

Eave length is the run of roof edge that gets soffit and fascia.

Prices (optional)

$
$
$
$
$
$
$

Squares of siding (with waste)

–

Boxes to buy
–
Wall area to cover
–
Outside corner posts
–
Material cost
–

An estimate for quoting and buying. Housewrap, flashing, nails, inside corners, window trim and utility blocks are not included; the siding maker's instructions and your local code win.

Squares are 100 sq ft of wall. Labor is priced on the net wall area, without waste.

The calculation runs in your browser and ParrotNotes does not store your numbers. They sit in the page address so you can bookmark or share the result.

How to measure a house for siding

Measure each wall's width and height from the bottom of the siding to the eave. For a plain box house the walls are 2 × (length + width) × height. Each gable is a triangle: base × height ÷ 2. Take off the windows and doors, then add a margin for cuts before you divide by what one box or plank covers.

Worked example: a 40 × 30 ft house with 9 ft walls has 1,260 sq ft of wall. Two gables 30 ft wide and 8 ft high add 240 sq ft. Ten 3 × 5 ft windows and two 36 × 80 in doors take off 190 sq ft, leaving 1,310 sq ft. With 10 % waste that is 1,441 sq ft, or 14.41 squares.

Squares, boxes and planks

Siding is sold and quoted by the square: 100 sq ft of wall. Vinyl usually comes 2 squares to a carton (Owens Corning packs its Reliance siding that way, with 12 ft 6 in panels for double 4 in), so the example house needs 8 boxes.

Lap planks depend on the exposure, the part of each plank that shows. James Hardie's chart lists 12 ft planks with 1¼ in of overlap: a 5¼ in plank shows 4 in, an 8¼ in plank 7 in, a 12 in plank 10¾ in. An 8¼ in plank covers 7 sq ft, so the example takes 206 planks. The maker's chart does not include waste.

Trim: corners, J-channel and starter strip

CertainTeed's measuring guide puts starter strip along the base of the building, J-channel around doors and windows, under eaves and at the rake edges of gables, and corner posts along each outside corner. The calculator adds the window perimeters, the sides and head of each door and, if you switch it on, the gable rakes, then rounds up to whole pieces.

In the example that is 4 corner posts of 10 ft, 261 ft of J-channel (23 pieces of 12.5 ft with waste) and 134 ft of starter strip (13 pieces of 12 ft). Piece lengths vary by maker; edit them to what your supplier stocks.

Pricing a siding quote

A siding quote is usually material plus labor per square. Enter your price per box or plank and per trim piece, and your labor rate per square; the calculator prices labor on the net wall area, without waste, and shows material and labor apart so you can see both on the quote.

Prices vary by region, profile and season, so the calculator ships with none. Get the yard's current price and check that the quote covers what the calculator leaves out: housewrap, flashing, fasteners, window trim, tear-off and disposal.

Tips for the walk-around

Measure every wall, count the windows and doors by size, note the gables, dormers and porches, and check the sheathing for soft spots. Building codes vary by place, and the local code and the siding maker's installation instructions win over any calculator.

Then write down what the homeowner told you: the profile and colour they like, trim and soffit wishes, which side gets the weather, budget and timing. Those notes win the job as much as the square count does.

Sources, checked October 2026. All figures are estimates:

More for roofing, siding and home-services sales: Roofing sales training, Door-to-door sales, Building materials sales.

The squares are only half the quote

The squares go on the quote. What the homeowner said on the walk-around about the profile and colour, trim, rotten sheathing, which side to start and when it has to be done goes in ParrotNotes: record the visit and get the summary and next steps.

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