Siding Calculator
Estimate siding for a house: wall and gable area into roofing-style squares, then vinyl panels or lap planks by their exposed coverage.
How siding is counted
Siding is sold by the square — 100 sq ft of covered wall — and the count starts from honest wall area: the perimeter times the wall height, plus the two gable triangles if your roof has them. Gables are figured as one rectangle of gable width × gable height (two triangles of ½ × width × height each).
Area = perimeter × wall height + gable width × gable height · Squares = area ÷ 100 · Pieces = area ÷ coverage per piece
Example: a 30 × 24 ft house with 9 ft walls has 972 sq ft of wall — 9.72 squares exactly, 10.69 squares to order with the 10% allowance, which is 134 vinyl panels of double-4, or 6 cartons.
Coverage is about exposure, not board width
Lap siding overlaps, so a board covers only its exposed face: a double-4 vinyl panel shows 8 inches, a 6¼-inch fiber-cement plank typically shows 5. The piece counts here use the exposed coverage, which is where naive estimates go wrong — counting full board width understates a lap-siding order by 20% or more. Vinyl is also sold by the carton of 2 squares, and the result rounds you to whole cartons for that material.
Openings are not subtracted: windows and doors are normally covered by the waste allowance on real houses, and cutting around them is exactly what the allowance pays for. Trim, J-channel, starter strip and corner posts are separate line items at the supplier — bring your wall lengths and opening count and they will figure those from the same area.
Frequently asked questions
What is a square of siding?
100 square feet of covered wall — the unit siding is priced and ordered in, borrowed from roofing. A 2,000 sq ft house typically needs 18–22 squares once gables and waste are in.
How much waste should I allow for siding?
10% suits a simple rectangular house. Complex elevations with many corners, bump-outs and gables eat 12–15%, mostly in cuts that cannot be reused elsewhere on the wall.
Do I deduct windows and doors?
For an order estimate, trade practice is no — the openings' area roughly cancels against cutting waste and the pieces lost around them. For a very glassy wall, deduct the big openings yourself by entering a smaller height or perimeter.
Vinyl or fiber-cement — does the counting differ?
Only in the piece coverage: both are counted by exposed face. Fiber-cement planks come in 12 ft lengths like vinyl panels, but they are heavier and cut with more breakage, so stay at the top of the waste range with them.
CalcCoverage