How much siding do I need?
Siding is sold by the square, and one square covers 100 square feet. Total the wall area, subtract openings, add 10% waste, then divide by 100.
Wall area = perimeter × average height, plus gable triangles. Each gable is ½ × width × height — a 24 ft wide gable rising 8 ft adds 96 sq ft.
Worked example: a house with a 140 ft perimeter and 9 ft walls has 1,260 sq ft, plus 200 sq ft of gables = 1,460 sq ft. Subtract two doors and ten windows (192 sq ft) for 1,268 net. Add 10% and you need 13.9 squares.
Only subtract openings larger than about 10 square feet. Small windows do not save a usable piece of siding — the offcut is waste either way.
How the calculation works
Net area = (perimeter × height + gables) − openings. Squares = net × (1 + waste) ÷ 100.
Waste runs 10% for a simple rectangular house, and 15% or more for complex elevations with dormers, bays and multiple rooflines. Every direction change is another cut.
Trim is calculated separately and is easy to underestimate. Starter strip runs the full perimeter. J-channel goes around every window and door — roughly 16 linear feet per window and 19 per door. Corner posts run the full wall height at each outside corner.
Fiber cement is ordered by the piece rather than the square in many markets. A 12 ft plank at 7 in exposure covers 7 sq ft, so divide net area by 7 to get plank count.
Typical siding cost, mid-2026
| Material | Unit | Typical range |
|---|---|---|
| Vinyl siding | per square | $150 – $400 |
| Fiber cement (Hardie-type) | per square | $300 – $700 |
| Engineered wood | per square | $250 – $550 |
| Cedar lap | per square | $400 – $1,100 |
| Starter strip | per linear ft | $1.20 – $3.00 |
| J-channel | per linear ft | $1.50 – $4.00 |
| Outside corner post | per linear ft | $3.00 – $8.00 |
| House wrap | per square | $15.00 – $35.00 |
| Installed vinyl sidingLabour and materials | per sq ft | $4.00 – $9.00 |
What goes wrong on this job
- Do not subtract small windows. A 3 × 4 ft window does not yield a reusable piece of siding, so counting it as a saving leaves you short on the last wall.
- Nail vinyl siding loosely. It has to slide — vinyl expands and contracts up to ½ in over a 12 ft panel across the seasons, and nailing it tight causes the buckling you see on badly sided houses.
- Order all siding in one batch and check the lot numbers. Colour varies between production runs, and a wall sided from two lots shows the difference in direct sun.
- Fiber cement needs specific cutting gear and respiratory protection — the silica dust is genuinely hazardous. Budget for a shear or a dust-collecting saw rather than a standard circular saw.
- House wrap goes on before siding, every time. It is cheap, it is the actual weather barrier, and retrofitting it means taking the siding back off.
Frequently asked questions
How many square feet in a square of siding?
100 square feet. Siding, roofing and some other exterior materials are all sold in squares.
How do I calculate gable siding area?
Each gable is a triangle: ½ × base width × height. A gable 24 ft wide rising 8 ft to the peak is 96 sq ft. Add each gable to the wall total.
How much waste should I allow for siding?
Ten percent for a simple rectangular house, 15% for complex elevations with dormers, bays or multiple rooflines.
Should I subtract windows and doors from siding area?
Subtract anything over about 10 sq ft. Smaller openings do not produce reusable offcuts, so subtracting them makes the order short.