How Much Siding Do I Need?
The one-number answer, in squares: your total wall and gable area, minus the doors, windows and garage openings, times a waste factor — rounded up. One square = 100 sq ft.
This house needs about 15 squares of siding — the one-number “how much siding do I need” answer: total wall and gable area minus the openings, times a waste factor, in squares (1 square = 100 sq ft). Complex layouts, corners and shingles use more, so measure your actual walls and gables and follow the manufacturer’s coverage; round up to whole squares.
1 Enter your numbers
“How much siding do I need?” has one honest answer, and it is a number of squares. A square is the trade unit for siding: exactly 100 square feet of finished wall. Siding is ordered, quoted and priced by the square, so converting your house into squares is the step that turns a wall into a materials list and a budget.
This calculator does the whole conversion in one pass. It builds the gross area from two shapes — the rectangular walls (perimeter × height) and the triangular gables (½ × base × height each) — subtracts the openings you will not side (doors, windows, garage doors) to get the net area, applies a waste factor for cuts and offcuts, divides by 100, and rounds up to whole squares. Every intermediate value is shown in the readout so you can check the arithmetic against your own tape measure.
Why squares, and why round up
Rounding up is not padding — it is a constraint. You cannot buy 14.7 squares; the supplier sells whole boxes and bundles, and a job that runs one panel short at the last corner stalls for a re-order. The waste factor and the ceiling to whole squares together absorb the cuts you make at corners, gables, openings and the last course, plus a small margin for damaged pieces. Order the whole squares and keep the offcuts for future repairs.
Formula
net_area = (perimeter × wall_height) + Σ(½ × gable_base × gable_height) − Σ openings
squares = ⌈ net_area × (1 + waste%) ÷ 100 ⌉
Openings use labeled standard deductions — door ≈ 21 sq ft, window ≈ 15 sq ft, double garage door ≈ 112 sq ft — which you should replace with your measured sizes when they differ. The ⌈ ⌉ brackets mean “round up to the next whole square.” 1 square = 100 sq ft, always.
Worked example
Take a two-gable house: a 140 ft perimeter with 10 ft walls, two gables each 30 ft wide and 8 ft tall, with 10 windows, 2 doors and 1 double garage door, at a 10% waste factor.
- Walls: 140 × 10 = 1,400 sq ft
- Gables: 2 × (½ × 30 × 8) = 2 × 120 = 240 sq ft
- Gross: 1,400 + 240 = 1,640 sq ft
- Openings: (10 × 15) + (2 × 21) + (1 × 112) = 150 + 42 + 112 = 304 sq ft
- Net: 1,640 − 304 = 1,336 sq ft
- With 10% waste: 1,336 × 1.10 = 1,469.6 sq ft → ⌈14.70⌉ = 15 squares
So this house needs about 15 squares of siding. That same 1,336 sq ft is the base every cost tool on this site starts from.
Measure first, avoid a re-order
- Walk the perimeter at ground level and add every wall length; do not estimate from the floor plan, which ignores bump-outs and offsets.
- Measure wall height to the soffit, not to the peak. The gable triangles are counted separately — counting them twice is the most common over-order.
- Add every gable and dormer. A complex roofline hides a surprising amount of triangular wall.
- Complex layouts use more. Many corners, gables, dormers or a diagonal/shingle pattern push waste toward 12–15%+; a plain rectangle sits near 10%. Adjust the waste factor to your house.
- Round up, keep the extra. Offcuts are your future repair stock; a color or lot match years later is rarely possible.
Reference table
Labeled planning typicals — measure your actual openings. Subtract these from the gross wall + gable area.
| Opening | Deduct (sq ft) |
|---|---|
| Standard door (3 × 7) | 21 |
| Standard window | 15 |
| Patio / sliding-glass door | 40 |
| Single garage door (9 × 7) | 63 |
| Double garage door (16 × 7) | 112 |