How Much Siding Do I Need? Squares, Openings & a Worked Example

Planning estimate, not a contractor quote. Siding is sold by the square, and the count is gross wall area minus openings plus waste — with gables as the classic miss. This guide gives you the method — then run your house through our siding calculator.

The square

One square of siding = 100 sq ft of wall it covers — the unit suppliers quote for vinyl, fiber cement, and most other siding. (A roofing square is also 100 sq ft, but roofing is measured on the slope; siding counts flat wall area.) The formula: squares = (gross wall area − openings) × (1 + waste) ÷ 100, rounded up to whole squares for ordering.

Measuring walls

Measure every exterior wall (width × height) and add them up. A 60 ft wall at 8 ft high is 480 sq ft. For a rectangular house, that is 2 × (length + width) × height — but do not use floor area as a shortcut: walls are usually 40–60% of floor area for a single-story home and far more for a two-story, because the walls are twice as tall around a smaller footprint. Measure the walls themselves.

Deducting openings

Subtract about 21 sq ft per exterior door (3 × 7 ft) and about 12–15 sq ft per standard window. These are planning figures, close enough because the waste allowance absorbs the difference — but measure oversized doors, sliders, and picture windows exactly, and if you plan to trim around openings, subtract a little less, since trim covers some of the opening area anyway.

Gables and waste

Gable triangles add real area: base × height ÷ 2 per triangle, added to the gross wall area. Houses with many gables, dormers, and openings should use 15% waste; simple rectangular houses can hold 10%. Long runs mean planks rarely end clean at a corner — 10% waste is the floor, not the ceiling, and complicated rooflines push it up, never down.

Worked example: 1,500 sq ft ranch

Gross wall area. Roughly 1,826 sq ft of wall for a typical 1,500 sq ft single-story ranch.
Squares net. 1,826 ÷ 100 = 18.3 squares.
With waste. 1,826 × 1.10 = 2,008.6 sq ft ÷ 100 = 20.09 → order 21 squares.
Trim. Budget roughly 10–15% extra of the siding cost for corner posts, J-channel, and starter strips.

Buying by type

The square count is the same for every siding type, but how you buy differs: vinyl and aluminum are sold by the square in cartons, while fiber cement and wood lap siding are sold by the plank or board — divide the order area by your product's coverage per piece. Installed siding in 2026 typically costs $4–$20 per sq ft depending on material (vinyl $4–$8, fiber cement $8–$14, wood and metal $10–$20), including labor and trim.

Frequently asked questions

How much siding do I need for a 1,500 sq ft house?

A 1,500 sq ft single-story ranch has roughly 1,826 sq ft of wall — about 18.3 squares net, so order 21 squares with a 10% waste allowance.

What is a square of siding?

One square = 100 square feet of wall coverage — the standard unit vinyl, fiber cement, and most other siding types are sold in.

How much siding do I subtract for windows and doors?

About 21 sq ft per exterior door (3 × 7 ft) and about 12–15 sq ft per standard window. If you plan to trim around openings, subtract a little less.

Do gables need extra siding?

Yes — gable triangles add area. Measure each triangle (base × height ÷ 2) and add it to the gross wall area; houses with many gables should use 15% waste.

How many squares of siding for a 2,000 sq ft house?

A 2,000 sq ft two-story house typically needs 24–28 squares — its exterior walls total roughly 2,400–2,800 sq ft depending on footprint, before waste.

The rest of the exterior job

Siding is one exterior system — pair it with roofing squares for the roof and paint for trim and accents when budgeting the whole exterior.