Siding is ordered in squares, and one square covers 100 sq ft of wall. Multiply your perimeter by the wall height, add the gables, subtract large openings, divide by 100 and add 10 to 15% for waste. A two-story 30 × 50 ft house has about 2,805 sq ft of net wall, or 28 squares, so you'd order 32 with 12% waste.
A square is 100 sq ft of wall coverage. It's the unit suppliers quote and the unit most siding is priced in, the same convention roofers use. So 1,500 sq ft of wall is 15 squares, and a quote of $350 a square works out to $3.50 per sq ft of wall for the material alone.
The job of estimating is turning your house into that one number, then adding enough extra that you don't run short on the last wall.
You need four measurements, and a tape measure and a notepad will get you all of them in half an hour.
Then: (perimeter × height + gables − openings) ÷ 100 = squares. Multiply by 1 plus your waste factor and round up. That's exactly what our siding calculator does.
Worked through for a two-story 30 × 50 ft house: 160 × 18 = 2,880 sq ft of wall. Add two 30 ft gables at 225 sq ft total, take off 300 sq ft of windows and doors, and you're at 2,805 sq ft, or 28.05 squares. With 12% waste that's 31.4, so you order 32 squares.
A gable is a triangle, so its area is half the base times the height. The base is the width of that end wall. The height depends on the roof pitch: gable height = (width ÷ 2) × (pitch rise ÷ 12).
If you don't know the pitch, our roof pitch calculator will work it out from a rise and run measurement. Here's how much wall one gable adds at common widths and pitches:
| Gable width | Roof pitch | Gable height | Area of one gable | Two gables |
|---|---|---|---|---|
| 24 ft | 4/12 | 4.0 ft | 48 sq ft | 96 sq ft |
| 24 ft | 6/12 | 6.0 ft | 72 sq ft | 144 sq ft |
| 28 ft | 6/12 | 7.0 ft | 98 sq ft | 196 sq ft |
| 30 ft | 6/12 | 7.5 ft | 112.5 sq ft | 225 sq ft |
| 30 ft | 8/12 | 10.0 ft | 150 sq ft | 300 sq ft |
| 32 ft | 12/12 | 16.0 ft | 256 sq ft | 512 sq ft |
Steep roofs change the order a lot. A pair of 12/12 gables on a 32 ft house adds more than 5 squares on their own. Hip roofs have no gables at all, which is why the smallest house below has a zero in that column.
These rows run the calculator's formula on common house shapes with a 12% waste factor, the tool's default. Gables assume a 6/12 roof on the short ends.
| House | Perimeter × height | Gables | Openings | Net wall area | Squares | Order (12% waste) |
|---|---|---|---|---|---|---|
| 30 × 30 ft, 1-story, hip roof | 120 × 9 ft | 0 | 120 sq ft | 960 sq ft | 9.60 | 11 |
| 30 × 40 ft, 1-story | 140 × 9 ft | 225 sq ft | 150 sq ft | 1,335 sq ft | 13.35 | 15 |
| 30 × 50 ft, 1-story | 160 × 9 ft | 225 sq ft | 180 sq ft | 1,485 sq ft | 14.85 | 17 |
| 30 × 50 ft, 2-story | 160 × 18 ft | 225 sq ft | 300 sq ft | 2,805 sq ft | 28.05 | 32 |
| 40 × 60 ft, 2-story | 200 × 18 ft | 400 sq ft | 400 sq ft | 3,600 sq ft | 36.00 | 41 |
A typical one-story ranch lands between 11 and 17 squares. Most two-story homes need 30 to 40. At the calculator's default of $350 a square, the 32-square order is $11,200 in field material before trim, wrap and labor.
Waste covers the cuts around windows, the offcuts at corners and gables, and the odd damaged piece. The more corners and openings, the more you throw away.
| Waste factor | Good for | Order for the 2,805 sq ft house |
|---|---|---|
| 5% | Plain rectangle, few windows, experienced installer | 30 squares |
| 10% | Simple one-story, average number of windows | 31 squares |
| 15% | Two-story, lots of windows, some gables | 33 squares |
| 20% | Complex roofline, dormers, diagonal cuts | 34 squares |
Going from 5% to 20% adds 4 squares here, which is about $1,400 at $350 a square. That sounds like a lot, but running short is worse. Siding is made in batches, and a reorder weeks later may not match the color of what's already on the wall, especially with vinyl and prefinished fiber cement.
Partly. Big openings like garage doors and sliding patio doors should come off, because they're whole squares of wall you won't cover. Small windows are different. The pieces you cut to go around them usually can't be reused anywhere, so a 3 × 4 ft window saves much less than its 12 sq ft.
A common approach is to subtract garage doors and large glass fully, subtract ordinary windows, and keep your waste factor at the higher end of the range. Or skip subtracting small windows entirely and use a lower waste factor. Either gets you close. What you shouldn't do is subtract every opening and then use 5% waste.
The field siding is only part of the order. Trim and accessories are sold by the piece or the linear foot, so measure them separately.
Installation details vary by material, and they matter for the warranty. Vinyl gets nailed in the center of the slots no more than 16 in apart, and the nail heads shouldn't be driven tight, so the panel can move with temperature. Fiber cement like James Hardie wants clearance off the ground (about 6 in) and off roof lines (1 to 2 in). Read the manufacturer's installation guide before you order fasteners, not after.
Planning to paint instead of replace? The paint calculator uses the same wall-area math to work out gallons.
It depends on wall area, not floor area. A 2,000 sq ft two-story home might have 2,200 to 2,800 sq ft of wall, which is 22 to 28 squares before waste, or about 24 to 32 squares with 10 to 15% added. Measure the perimeter and wall height to get a real number.
One square of siding covers 100 sq ft of wall. To convert, divide your wall area in square feet by 100. So 1,485 sq ft of wall is 14.85 squares, and you'd order 17 with 12% waste.
Multiply the gable's width by its height and divide by 2. The height is half the width times the roof pitch rise over 12. A 30 ft wide gable on a 6/12 roof is 7.5 ft tall, so it's 30 × 7.5 ÷ 2 = 112.5 sq ft.
Add 10% for a simple one-story house, 15% for two stories or lots of windows, and up to 20% for complex rooflines with dormers and diagonal cuts. Round the total up to whole squares. It's cheaper than a reorder that may not match in color.
Subtract large openings like garage doors and patio doors. Small windows save less than their size suggests, because the cut pieces around them are usually waste. Many estimators leave small windows in and use a lower waste factor, which lands in about the same place.