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Construction & Home
Siding Calculator — How Many Squares of Siding You Need
How many squares of vinyl, lap or board siding for your walls
A siding calculator turns your wall measurements into the number that matters at the supply desk: how many squares of siding to order. In the siding and roofing trades a "square" is not a shape — it's a unit of coverage equal to 100 square feet. Vinyl, fiber-cement, board-and-batten and aluminum siding are all sold and quoted by the square, so the job is to find your total wall area, knock out the openings, add a waste cushion, and round up to whole squares — because you can't order a partial box.
The math starts the same way as paint, but the unit is different. First find the gross wall area: for each wall, length × height, all in feet. A house with four 40 ft × 9 ft walls is 4 × (40 × 9) = 1,440 square feet of gross wall.
Next, subtract the openings you won't side over. You don't side across doors and windows, so deduct them:
- Exterior door ≈ 21 sq ft (a standard 3 ft × 7 ft door)
- Window ≈ 15 sq ft (a typical 3 ft × 5 ft window)
Say that house has 2 doors and 7 windows: 2 × 21 + 7 × 15 = 42 + 105 = 147 sq ft of openings. Net wall area = 1,440 − 147 ≈ 1,293 sq ft.
Now convert to squares and add waste:
• Squares = net area ÷ 100 × (1 + waste). At 1,293 sq ft that's 12.93 squares before waste.
• Waste factor: the default is 10%, which covers normal trim cuts and offcuts. Bump it to 15% for lap siding or complex walls — clapboard, Dutch lap, board-and-batten, lots of corners, gables and dormers all create more cut-off because each course has to be trimmed to length around openings and corners.
13.05 squares (the rounded 1,305 sq ft figure from a clean four-wall estimate) × 1.10 ≈ 14.4, which rounds up to 15 squares. That extra cushion isn't waste you throw away — it's the offcuts, the miscuts, and the spare pieces you keep for repairs after a storm.
This calculator lets you enter walls one at a time (so you can add gable ends and bump-outs), set the door and window counts, choose a waste factor, and optionally enter a price per square for a fast material estimate. It is built for siding on walls — distinct from a paint calculator, which measures coverage in gallons, and from a roofing calculator, which counts squares on the roof slope instead of the walls.
📖 See also: How to Calculate a Tip (and Split the Bill)
Calculator
Fill in the fields and click "Calculate" for instant results.
📰 Formula
• Gross wall area (sq ft) = sum of each wall's length (ft) × height (ft) • Openings (sq ft) = doors × 21 + windows × 15 • Net wall area = gross wall area − openings • A siding square = 100 sq ft • Squares = (net area ÷ 100) × (1 + waste% ÷ 100), rounded up • Opening sizes used: exterior door = 21 sq ft (3×7) · window = 15 sq ft (3×5) • Waste factor: 10% standard · 15% for lap siding or complex walls
📰 Formula
• Gross wall area (sq ft) = sum of each wall's length (ft) × height (ft) • Openings (sq ft) = doors × 21 + windows × 15 • Net wall area = gross wall area − openings • A siding square = 100 sq ft • Squares = (net area ÷ 100) × (1 + waste% ÷ 100), rounded up • Opening sizes used: exterior door = 21 sq ft (3×7) · window = 15 sq ft (3×5) • Waste factor: 10% standard · 15% for lap siding or complex walls
🧪 Worked examples
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Example 2
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Example 3
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Example 4
⚠️ Common mistakes
- Forgetting to subtract doors and windows, so you over-order squares for area you never side.
- Measuring height to the eave only and skipping the triangular gable area above it.
- Using a 10% waste factor on lap or board-and-batten — those need about 15% for trim cuts.
- Quoting square feet to the supplier when siding is sold by the square (100 sq ft).
- Rounding squares down — you can't buy a partial box, always round up.
💡 Tips
- Add a wall row for each gable: a gable triangle is (base × height) ÷ 2 above the wall it sits on.
- Keep the leftover squares from your waste cushion — matching siding for storm repairs is hard to source later.
- For Dutch lap, clapboard and board-and-batten, set waste to 15% because every course is cut to length.
- Order trim, J-channel and corner posts separately — this counts field siding, not accessories.
- Measure to the nearest half-foot and add waste before rounding, so the cushion survives the round-up.
Embed this calculator on your site
Copy the code below and paste it into the HTML of your site or blog.
<iframe src="https://www.calcnimbus.com/embed/siding-calculator" width="100%" height="500" frameborder="0" style="border:1px solid #eee;border-radius:12px"></iframe>
❓ Frequently asked questions
How much siding do I need for my house?
Add up each wall's length × height in feet, subtract about 21 sq ft per door and 15 sq ft per window, divide by 100 to get squares, then add 10% waste and round up. A 1,300 sq ft net wall is about 15 squares with waste.
What is a square of siding?
A square is the trade unit for siding and roofing and equals 100 square feet of coverage. Vinyl, fiber-cement and board siding are ordered by the square, so 15 squares covers 1,500 square feet of wall.
How many square feet are in a square of siding?
Exactly 100 square feet. To convert, divide your net wall area by 100. A wall of 480 square feet is 4.8 squares before waste, which rounds up to 5 or 6 squares depending on the waste factor.
Do I subtract windows and doors when calculating siding?
Yes. You don't side over openings, so deduct them. This calculator uses about 21 sq ft for a standard exterior door and 15 sq ft for a typical window, then subtracts the total from your gross wall area.
How much extra siding should I buy for waste?
A 10% waste factor is the standard cushion for straight walls. For lap siding, clapboard, Dutch lap or complex walls with many corners and gables, use 15% because each course must be cut to length.
How do I calculate siding for a gable end?
Side the rectangular wall as length × height, then add the gable triangle above it: (base × height of the triangle) ÷ 2. Enter the triangle as its own wall row so it's included in the square count.
How many squares of vinyl siding are in a box?
A typical box of vinyl siding covers about 2 squares (200 sq ft), though it varies by brand and profile. Order enough boxes to meet your square count, then round up to whole boxes at the store.
How much does a square of siding cost?
Material runs roughly $150 to $400 per square for vinyl and more for fiber-cement, before labor. Enter your local price per square in the calculator to get a quick material estimate for the whole job.
Is a siding calculator the same as a paint calculator?
No. A siding calculator counts squares of material (100 sq ft each) for the walls, while a paint calculator converts the same area into gallons based on coverage per gallon. Use this for siding, the paint calculator for paint.