Roofing & Exterior
Siding Calculator
Calculate how much siding you need for your house. Enter each wall and gable, subtract doors and windows, and this siding calculator gives the net square footage, siding squares, boxes to buy and an optional cost for vinyl and other siding.
Result
Enter your measurements and press Calculate. What to buy, the working and the cost will appear here.
How to use the siding calculator
- Enter each wall: its length and height from the bottom of the siding to the eave.
- Add gables, the triangles above the walls at gable ends, with their width and height to the peak.
- Subtract doors and windows as one total area.
- Set the waste and box coverage, add a price per square or box, and press Calculate.
How much siding do I need?
wall area = Σ (length × height) + Σ (½ × gable width × gable height) − openings
squares = wall area × (1 + waste) ÷ 100
A 40 × 28 ft one-story house with 9 ft walls has 1,224 ft² of wall. Two 28 ft gables 7 ft high add 196 ft². Subtract 210 ft² of doors and windows and add 10%: about 13.3 squares.
Worked example: re-siding a ranch house
A 40 × 28 ft ranch house with 9 ft walls, two 7 ft high gables, 210 ft² of doors and windows, vinyl siding at $120 per square:
- Wall 1: 40 ft × 9 ft × 2 = 720 ft²
- Wall 2: 28 ft × 9 ft × 2 = 504 ft²
- Gable 1: ½ × 28 ft × 7 ft × 2 = 196 ft²
- Net area: 1,420 ft² − 210 ft² = 1,210 ft²
- Boxes: 1,210 ft² × 1.1 = 1,331 ft² ÷ 200 ft² → 7 boxes
Siding squares: 13.31; Boxes: 7 boxes; Net wall area: 1,210 ft²; Estimated cost: $1,597.20. Open this example in the calculator.
Siding squares and boxes
Like roofing, siding is sold by the square (100 ft²). Vinyl siding usually comes in boxes of two squares; fiber cement and wood siding are sold by the piece, so convert the area using the exposure (the visible width of each board) shown on the product.
How much extra siding?
- 10% for simple rectangular houses.
- 15% for houses with many corners, gables, bump-outs and openings.
- Don’t subtract every small window: cutting around small openings often wastes most of the piece, so many installers only subtract large openings such as garage doors.
Trim and accessories
Siding also needs starter strip along the bottom, outside and inside corner posts, J-channel around windows and doors, finish trim under the eaves and soffit and fascia. These are measured in linear feet; the linear feet calculator helps add them up.
Assumptions and limitations
- Walls are rectangles and gables triangles; dormers and bay windows can be added as extra walls.
- Box coverage comes from you; 2 squares per box is a common vinyl default.
- House wrap, insulation board and fasteners are not included.
Siding questions
How do I calculate siding squares?
Multiply each wall’s length by its height, add the gable triangles, subtract doors and windows, add 10% and divide by 100.
How many squares of siding for a 2,000 square foot house?
It depends on wall height and shape rather than floor area, but a 2,000 ft² two-story house often has 2,000–2,500 ft² of wall: around 20–28 squares with waste.
How many boxes of vinyl siding do I need?
Divide the squares by the squares per box, usually 2. 13.3 squares is 7 boxes.
Formulas, unit conversions and default values are explained on our methodology page. Results are estimates; check manufacturer data and local codes before you buy or build.