Siding is sold by the square, which is 100 ft² of wall coverage, the same unit used for roofing. To order it you need the area of every wall, plus the triangular gable ends under the roof, minus the windows and doors, plus a waste allowance for cuts and laps. This siding calculator does all of that from a few house measurements, then converts the result to squares, boxes and the starter strip and corner posts you'll need. A 40 × 30 ft house with 9 ft walls and two 6/12 gables comes to about 13.9 squares, or 7 boxes of a typical 2-square carton.
The roof uses the same squares: see the roofing shingles calculator. Replacing sheathing too? The plywood & osb sheathing calculator counts sheets.
How to use the siding calculator
- Enter the house length, width and wall height from the foundation or starter line up to the eaves.
- Enter the number of gable ends, their width and the roof pitch. A 6/12 pitch rises 6 inches per foot of run.
- Count windows and doors and enter average sizes. A typical 3 × 5 ft window is 15 ft²; a standard entry door with trim is about 21 ft².
- Use 10% waste for a simple rectangle, 15% or more for many corners, dormers or bump-outs.
- Enter the squares per box from the product listing to get a carton count.
Formula
Worked example
A 40 × 30 ft house with 9 ft walls, two 30 ft wide gables at 6/12, 12 windows of 15 ft², 2 doors of 21 ft² and 10% waste.
- Walls: 2 × (40 + 30) × 9 = 140 × 9 = 1,260 ft².
- Gables: rise = 15 × 6 ÷ 12 = 7.5 ft; each gable 30 × 7.5 ÷ 2 = 112.5 ft²; two = 225 ft².
- Openings: 12 × 15 + 2 × 21 = 222 ft². Net: 1,260 + 225 − 222 = 1,263 ft².
- With 10%: 1,389 ft² = 13.9 squares, so order 14 squares or 7 boxes of 2.
- Starter strip: 140 ft ÷ 12 = 12 pieces. Corners: 4 posts of 10 ft.
Squares of siding by house size
Walls only (no gables), no openings deducted, 10% waste. Add your gables from the second table.
| House footprint | 8 ft walls | 9 ft walls | 10 ft walls |
|---|---|---|---|
| 24 × 24 ft | 8.4 | 9.5 | 10.6 |
| 24 × 36 ft | 10.6 | 11.9 | 13.2 |
| 28 × 40 ft | 12.0 | 13.5 | 15.0 |
| 30 × 50 ft | 14.1 | 15.8 | 17.6 |
| 40 × 60 ft | 17.6 | 19.8 | 22.0 |
Gable area by span and pitch
Area of one triangular gable end.
| Gable span | 4/12 pitch | 6/12 pitch | 8/12 pitch | 12/12 pitch |
|---|---|---|---|---|
| 24 ft | 48 ft² | 72 ft² | 96 ft² | 144 ft² |
| 28 ft | 65 ft² | 98 ft² | 131 ft² | 196 ft² |
| 30 ft | 75 ft² | 113 ft² | 150 ft² | 225 ft² |
| 36 ft | 108 ft² | 162 ft² | 216 ft² | 324 ft² |
| 40 ft | 133 ft² | 200 ft² | 267 ft² | 400 ft² |
Steep gables add a lot: a 30 ft gable at 12/12 is 225 ft², twice the area of a 6/12 gable of the same width.
Trim, accessories and code
Besides panels, siding needs starter strip along the bottom, outside and inside corner posts, J-channel around windows, doors and the roofline, utility trim under windows and soffits, and fasteners. Accessory lengths vary by brand, so this calculator counts only starter strip (12 ft pieces) and corner posts (10 ft pieces); measure window and door perimeters for J-channel. The Vinyl Siding Institute's installation manual explains fastening and expansion gaps, and Chapter 7 of the International Residential Code covers water-resistive barriers and flashing behind any siding. Seal penetrations with the caulk calculator, and if you're painting existing siding instead, use the paint calculator. Adding exterior foam board under new siding? Size it with the insulation r-value calculator.
Caveats and assumptions
- Openings are often left out of rough estimates to cover waste; deducting them and adding a waste factor is more accurate.
- Dormers, bay windows, porches and chimneys add area and cuts. Measure them separately and add them to the walls.
- Fiber-cement, wood and engineered siding are sold differently (by piece or linear foot). Convert squares using the product's exposure and length.
- Accessory pieces vary in length by manufacturer; check before ordering.
Frequently asked questions
How many squares of siding do I need?
Divide the net wall area plus gables, with waste, by 100. A 1,500 ft² wall area needs 15 squares plus waste, about 16.5 squares at 10%.
What is a square of siding?
A square is enough siding to cover 100 ft² of wall. A box of vinyl siding commonly holds 2 squares, but check the product.
How do I calculate siding for a gable?
Find the rise (half the span × pitch ÷ 12), then multiply span × rise ÷ 2. A 30 ft gable at 6/12 rises 7.5 ft, so its area is 112.5 ft².
Should I subtract windows and doors from siding?
Yes for accuracy, then add 10–15% waste. Some estimators skip deducting small windows to cover extra cuts around them.
How much siding for a 2,000 sq ft house?
It depends on shape and wall height, not floor area. A two-story 25 × 40 ft house with 18 ft of wall height has 130 × 18 = 2,340 ft² of wall before gables and openings, about 25.7 squares with 10% waste.
Sources
- Polymeric Exterior Products Association (Vinyl Siding Institute) — Installation — installation manual and accessories
- ICC — 2021 International Residential Code, Chapter 7: Wall Covering — siding, water-resistive barrier and flashing requirements
- NIST — Unit Conversion — area units
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.