Siding Calculator

Siding area formula

Measure rectangular wall area, add triangular gables, subtract openings, then apply the chosen waste percentage:

wall area   = total wall length × average wall height
gable area  = 0.5 × gable base × gable height × gable count
gross area  = wall area + gable area
net area    = gross area - doors and windows
area to buy = net area × (1 + waste percentage / 100)
packages    = area to buy / coverage per package

The Vinyl Siding Institute defines one siding square as 100 ft². The calculator converts the order area to trade squares, but it uses your package coverage for the purchase count because coverage varies by product and profile. LP Building Solutions describes the wall, gable and opening method. NIST conversion factors are used for the imperial and metric results.

Worked example

Suppose the walls total 160 ft long and average 9 ft high. Two matching gables each measure 20 ft across and 6 ft high. Doors and windows cover 180 ft², waste is 10%, and one package covers 100 ft².

That is 15.18 squares or 15.18 packages at 100 ft² each, so 16 whole packages are needed. Those packages cover 1,600 ft², leaving an estimated 82 ft² above the calculated order area.

Check the product before ordering

• Use the manufacturer’s stated coverage for the exact profile, exposure and package. Ply Gem notes that actual exposure affects coverage.
• Waste depends on wall layout, cuts, pattern, installer practice and product guidance. Published examples often discuss 5% to 10%, but that is not a universal rule.
• Accessories such as starter strips, corner posts, trim, flashing and fasteners are not included here.
• Verify field measurements and local installation requirements before buying. If existing siding may contain asbestos, do not disturb it based on an online estimate. Follow EPA guidance and seek qualified help.