About the Siding Calculator
This siding calculator estimates how much vinyl, fiber-cement, wood or metal siding a house needs. Enter the total length of the exterior walls, the wall height, any triangular gable ends, and the number and size of windows and doors. It subtracts the openings, adds a waste allowance for cuts and overlaps, and converts the result into siding squares (100 square feet each), which is how siding is priced and ordered.
Homeowners use it to budget a re-side or check a contractor quote, and DIYers use it to know how many boxes to pick up. Vinyl siding is commonly sold in cartons that cover about two squares, so the calculator also shows a box count; check the coverage printed on the product you buy.
Trim pieces such as J-channel, corner posts, starter strip and soffit are ordered by the linear foot and are not included in the square count. A waste factor of 10% suits simple rectangular houses; use 12–15% for many corners, dormers or complex gables.
With the default inputs, the siding needed (incl. waste) is 16.2 squares. Change any value above to recalculate instantly.
How to use the siding calculator
- 1Measure the length of every exterior wall and add them together.
- 2Measure the height from the bottom course to the soffit or eave.
- 3Add gable ends with their base width and height to the peak.
- 4Count windows and doors and enter their average size.
- 5Set a waste allowance and your price per square to see squares, boxes and cost.
Formula and method
The rectangular part of the house is the total wall length multiplied by the wall height. Each gable end is a triangle, so its area is half its base times its height from the eave line to the peak. Doors and windows are subtracted using their count multiplied by an average size.
A waste percentage is then added for cutting around openings, overlaps and damaged pieces, and the result is divided by 100 because siding is sold by the square (100 sq ft). The box count assumes two squares per carton, which is typical for vinyl but varies by product.
- Perimeter
- Sum of all exterior wall lengths (ft)
- Height
- Wall height to be sided (ft)
- Openings
- Windows × average size + doors × average size (sq ft)
- Waste%
- Extra for cuts and overlaps
Worked examples
Ranch house with two gables
The walls are 160 × 9 = 1,440 sq ft and the two gables add 2 × ½ × 30 × 7.5 = 225 sq ft. Ten windows and two doors remove 192 sq ft, leaving 1,473 sq ft. With 10% waste that is 16.2 squares, or 9 boxes, costing about $5,671 at $350 per square.
10 ft walls, no gables, 12% waste
A 200 ft perimeter at 10 ft high is 2,000 sq ft. Fourteen windows (210 sq ft) and three doors (63 sq ft) leave 1,727 sq ft; adding 12% waste gives 19.34 squares, about 10 boxes and $5,803 at $300 per square.
Frequently asked questions
What is a square of siding?+
A square is 100 square feet of wall coverage. Siding, like roofing, is priced and ordered by the square, so 1,500 sq ft of wall needs 15 squares before waste.
How much waste should I add for siding?+
Around 10% is common for simple rectangular houses. Add 12–15% for houses with many corners, bump-outs, dormers or steep gables, because every angled cut creates offcuts.
Should I subtract windows and doors?+
Yes for large openings such as doors, patio doors and garage doors. Many installers skip subtracting small windows because the offcuts rarely get reused, which gives a built-in safety margin.
How many boxes of vinyl siding do I need?+
Divide the squares by the coverage per box. Most vinyl siding cartons cover about two squares (200 sq ft), but check the label because coverage depends on profile and panel length.
Does this include trim and accessories?+
No. J-channel, starter strip, corner posts, soffit, fascia and house wrap are ordered separately, usually by linear foot of edges, corners and eaves.