Siding Squares Calculator: Wall Area to Cartons

Siding squares start with wall area, then the openings question

A siding square is 100 sq ft. James Hardie prints it in its own estimating guide header.

Read your own maker on this. Hardie labels the column coverage area less openings, so on fiber cement you deduct windows and doors. Kaycan tells vinyl estimators the opposite: do not deduct, because leaving the openings in is what pays for cutting waste.

Wall area is perimeter times wall height, plus a triangle for each gable. A gable triangle is half the width times the rise, and the rise is half the width times the pitch.

Worked example: a 40 by 28 ranch

Perimeter is 136 ft. At a 9 ft wall that is 1,224 sq ft. Two 6/12 gables 28 ft wide rise 7 ft, so each is 98 sq ft and the pair adds 196 sq ft. Gross is 1,420 sq ft.

Now deduct. Eight windows at 3 ft by 4 ft is 96 sq ft, and one door is about 20 sq ft. Net is 1,304 sq ft, or 13.04 squares.

SimplyWise Cost Estimator turns a photo into an itemized, branded estimate in about 6 seconds.

Carton coverage is not two squares by default

Most vinyl lines run two squares to a carton. Insulated lines do not, and one does not even hold a whole square.

Run the ranch through that. On Odyssey Plus double 4 at two squares per carton, 13.04 divided by 2 is 6.52, so 7 cartons. Prodigy double 6 at one square comes to 14 cartons. The dutch lap at 0.97 gives 13.44, so 14 cartons again.

What double 4 actually means

Profile names are exposure shorthand. Double 4 is two 4 in courses on one panel, so 8 in of exposure. That is our arithmetic off Alside’s published coverage, not a line from their catalog. Double 5 lands on 10 in, the insulated double 6 on 12 in.

Fiber cement counts planks, not cartons

HardiePlank comes in 12 ft lengths, in nominal widths from 5.25 in to 12 in, giving exposures from 4 in to 10.75 in. Hardie publishes the plank count per square for each width.

Wider boards cut the plank count hard, which is fewer laps, fewer nails, and fewer hours. Hardie also sets a 1.25 in minimum overlap and studs at 24 in on center max.

Trim is a linear foot line

The ranch has 136 ft of starter around the base. Alside aluminum starter comes 10 ft to the piece, so 13.6 pieces, meaning 14.

The eight windows and the door come to about 129 linear ft of J-channel, which comes 12 ft 6 in to the piece, so 10.3 pieces, meaning 11. Fasteners follow the panel: CertainTeed sets its Monogram nail slots at 16 in on center to hit studs, meeting IRC section R703.11.

About waste

A full-text search of the Alside catalog finds no waste percentage. Neither does the CertainTeed spec sheet. James Hardie says the quiet part plainly on its estimating chart: the plank counts do not include waste.

Kaycan is the exception: its 2025 guide multiplies each gable rectangle by 0.75 to allow for waste in cutting along the rake. The carton counts above are net of openings and carry no waste, so add your own line off gable cuts, corners, and course alignment.

Run it in this order

1. Take the wall band, then the gables

   Perimeter times wall height, plus half the width times the rise for each gable.

2. Settle the openings

   Deduct on fiber cement, per Hardie. Do not deduct on vinyl, per Kaycan.

3. Read the carton coverage off the catalog

   Two squares is common, not universal. Insulated lines can be one square or less.

4. Count trim in linear feet

   Base perimeter for starter, opening perimeters for J-channel, then round to whole pieces.