Siding Calculator: How Many Squares of Siding Do I Need?

Measure the length of every exterior wall you plan to side and add them together - for a simple rectangular house this is just the perimeter, so a 24x36 house has 24 + 36 + 24 + 36 = 120 feet of wall. Enter that total, then the wall height from the foundation line to the soffit (usually 8-9 feet for one story, 17-20 feet for two). Add how many doors and windows you have and the calculator subtracts a typical 3x7 ft door (21 sq ft) and 3x5 ft window (15 sq ft) for each. You instantly get the squares of siding to buy, with a 10% waste allowance already included. Open More options to add triangular gable ends, set exact door and window sizes, change the waste percentage, switch to metric, or enter a price per square for a material cost estimate.

Siding is sold and quoted by the square, and one square of siding equals 100 square feet of wall coverage. That is why a contractor will say a house "takes 18 squares" rather than 1,800 square feet. Vinyl siding is commonly packed 2 squares (200 sq ft) per box, while fiber cement, wood clapboard and engineered lap siding are often priced per square or per plank.

The area you need is the wall area you can actually see once the house is finished: the rectangular walls, plus the triangular gable ends under a pitched roof, minus the openings for doors, windows and garage doors. Many homeowners make the mistake of using the house's floor area ("how much siding for a 1,500 sq ft house?") - but floor area and wall area are different numbers. A 1,500 sq ft single-story home measuring 30x50 has 160 feet of wall; at 8 feet tall with two gables, two doors and twelve windows it needs roughly 15 squares after waste. Always measure the walls themselves.

Wall area = total wall length x wall height

Gable area = number of gables x (gable base width x gable height / 2)

Openings = (doors x area per door) + (windows x area per window)

Net area = wall area + gable area - openings

Total with waste = net area x (1 + waste % / 100)

Squares to buy = total with waste / 100, rounded up to a whole square

Vinyl boxes = squares / 2, rounded up

In metric mode the areas are calculated in m² and converted to square feet (1 m² = 10.7639 sq ft) before dividing by 100, because siding squares are a US unit.

Example 1 - single-story house, walls only: 160 ft of wall, 10 ft high, 2 doors, 10 windows.
Wall area = 160 x 10 = 1,600 sq ft. Openings = 2 x 21 + 10 x 15 = 192 sq ft. Net = 1,408 sq ft. With 10% waste = 1,548.8 sq ft = 15.49 squares, so buy 16 squares (8 boxes of vinyl).

Example 2 - how much siding for a 24x36 house with gables? Perimeter = 120 ft, 8 ft walls = 960 sq ft. Two gable ends 24 ft wide and 6 ft tall = 2 x (24 x 6 / 2) = 144 sq ft. Openings: 2 doors and 8 windows = 42 + 120 = 162 sq ft. Net = 960 + 144 - 162 = 942 sq ft. With 10% waste = 1,036.2 sq ft = 10.36 squares, so buy 11 squares (6 boxes).

Example 3 - one gable end only: A 28 ft wide gable rising 7 ft = 28 x 7 / 2 = 98 sq ft, about 1 square once waste is added.

- Use 10% waste for most homes. Go to 15% if the house has lots of corners, dormers or bump-outs, and 5% only for a plain rectangle.
- Do not over-deduct small windows. Many installers skip deducting openings smaller than about 10 sq ft because the cut-offs are rarely reusable.
- Measure gables separately. Measure the base width and the height from the top of the wall to the peak; the triangle is half of width x height.
- Keep a spare box. Siding colors and profiles get discontinued; an extra square stored in the garage makes future repairs match.
- Trim is extra. J-channel, starter strip, corner posts, soffit and fascia are bought by the linear foot and are not included in squares.
- Garage doors count. Enter a large garage door as several "doors" or set its exact area under More options.