How it works
The calculator adds up the walls and gables, subtracts doors and windows, adds your waste allowance and converts the result to squares.
Wall area = Total wall length × Wall height + Gable area
Net area = Wall area − Doors and windows
Squares = Net area × (1 + Waste ÷ 100) ÷ 100 sq ft
Pieces = ⌈ Net area × (1 + Waste ÷ 100) ÷ Coverage per piece ⌉
Squares are shown to two decimals so you can compare quotes; pieces and boxes are rounded up (⌈ ⌉) because you cannot buy part of one. In metric, a square is 100 sq ft = 9.29 m².
Coverage per piece has no default: it differs between profiles and makers. Enter the figure from your product’s label or data sheet. Trim and accessories are sold by length and need a separate estimate.
Worked example
Inputs
- Measure by
- Wall length × height
- Total wall length
- 140 ft
- Wall height
- 9 ft
- Gable area
- 0 sq ft
- Doors & windows (not covered) 1
- Width 3 ft, Height 4 ft, Count 10
- Doors & windows (not covered) 2
- Width 3 ft, Height 6 ft 8 in ft, Count 2
- Waste allowance
- 0 %
Result
- Wall area
- 1,260 sq ft
- Doors & windows
- 160 sq ft
- Area to side
- 1,100 sq ft
- Squares incl. waste
- 11
Common mistakes
- Forgetting the gables. The triangles above the eaves on gable ends can be a sizable share of the wall area.
- Subtracting every small opening. Vents and small fixtures are usually sided around, and subtracting them understates the material.
- Confusing a siding square with a roofing square bundle count. A siding square is 100 sq ft of wall, but how many pieces or boxes make one depends on the product.
- Leaving out trim and accessories. Corners, J-channel and starter strip are bought by length and are not part of the wall area.
Assumptions and limits
- In dimension mode, walls are treated as rectangles of total length × height; gables are added as an area you enter.
- Doors and windows are rectangles of width × height × count and are subtracted from the wall area.
- Squares are the net area including waste divided by 100 sq ft (9.29 m²). Pieces or boxes are rounded up to whole units.
- The estimate covers the wall siding only. It does not include trim, corners, J-channel, starter strip, housewrap or fasteners.
Frequently asked questions
What is a square of siding?
A square is 100 sq ft of wall. Ply Gem uses the same unit and notes that for double 4 in siding, 12 pieces cover about 1 square. Other profiles cover different areas per piece, so check your product.
Do I subtract windows and doors?
Yes, for full-size openings. Add a row for each opening size with the number of openings. Small vents and fixtures are usually sided around and are better left in.
How much waste should I add for siding?
It depends on the house shape, the number of openings and corners, and the product. Ask your siding maker or supplier for a figure; a plain wall with few openings needs less than a house with many gables and windows.
Sources
- How to Estimate Accessories for Your Siding Job — Ply Gem. For double 4 in siding, 12 pieces ≈ 1 square (100 sq ft); a square is 100 sq ft of wall.
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 2, 2026