A Free Tool · Walls & Openings · Measured in Squares
How much siding do you actually need?
Enter your total wall area, or measure up to four wall sections, subtract the big doors
and windows, and get the number of siding squares to order — plus
the underlying square footage. Siding, like roofing, is measured by the square
(100 sq ft), and a 10% waste factor for cuts and overlap is built in by default.
Squares & square feet·Total area or wall sections·1 square = 100 sq ft
Read this first
These are estimates based on the wall area you enter and a waste factor — not a
substitute for your own measurements or your product's spec sheet. Coverage per box or
panel varies by product and profile, so this tool stops at squares and square feet and
leaves the box count to the manufacturer's numbers. Always buy a little extra: an offcut
saved for a future repair is cheap, and dye lots can shift between orders. Confirm the
coverage on the actual product you buy.
The calculator
Estimate siding squares
Pick how you want to enter your walls — one total area, or up to four sections measured as length × height — then subtract big openings and set a waste factor. You'll get the squares to order plus the square footage behind them.
The combined area of every wall you're covering, before subtracting openings.
Add up big doors and windows. Small windows are often left in as part of the waste cushion.
10% for simple walls; 15% for lap siding or many corners and gables.
Gross wall area
Openings subtracted
Net wall area
Waste applied
Area with waste
Squares (100 sq ft each)
Squares to order (rounded up)
The math, honestly
How the squares are figured
It's all flat area. Your gross wall area is either the single number
you enter, or the sum of each wall section's length × height in
feet. Subtract the area of your big openings to get the
net wall area: net = gross − openings.
Then add a waste factor for cuts and overlap and convert to squares. Because a
square covers 100 square feet, the formula is
squares = net × (1 + waste/100) / 100, and you round that up to
whole squares to order. So 1,000 sq ft of net wall at 10% waste is
1000 × 1.10 / 100 = 11.0 squares — you order 11
squares.
Why the waste matters: siding is cut to fit around corners,
openings, and rooflines, and lap profiles overlap course to course. Ten percent
covers a simple, mostly rectangular wall; step up toward fifteen for lap siding or a
house with lots of gables, dormers, and trim. The coverage per box or panel is set by
the manufacturer, so this tool gives you squares and square feet and stops there.
Waste factor by siding and wall type
A reasonable starting waste factor depends on the siding profile and how cut-up the
walls are. These are starting points the calculator can use — bump them up for
steep gables, many windows, or fussy trim.
Situation
Typical wastestarting point
Why
Simple vinyl
10%
Interlocking panels on mostly rectangular walls waste little.
Lap siding
15%
Overlapping courses and corner cuts generate more offcuts.
Many corners / gables
15%
Angled cuts at rooflines and dormers can't always be reused.
Lots of windows / trim
12–15%
Cutting around each opening leaves harder-to-use pieces.
Waste is a cushion, not a precise figure. When several of these apply at once —
say, lap siding on a gabled house with lots of windows — lean toward the higher
end. This calculator defaults to 10% and lets you change it.
Common net areas in squares
Worked examples at a 10% waste factor, so they match what the calculator gives you. The
net area already has openings removed; squares-to-order is the rounded-up figure.
Net wall area
Area + 10% wastesq ft
Squaresexact
Squares to orderrounded up
1,000 sq ft
1,100
11.0
11
1,500 sq ft
1,650
16.5
17
2,000 sq ft
2,200
22.0
22
2,500 sq ft
2,750
27.5
28
The 1,000 sq ft row is the canonical worked example: 1,000 × 1.10 / 100 = 11.0
squares exactly, so you order 11. Whenever the exact figure lands above a whole number,
you round up to the next square.
Reading the result well
A square count is only useful if you act on it sensibly. Four things worth knowing
before you order.
Match the waste factor to the house
A box-shaped house with simple walls and few windows can run on 10% waste. A house with steep gables, dormers, bay windows, and lots of trim — or lap siding that overlaps course to course — generates more offcuts you can't reuse, so 15% is safer. The default here is 10%; raise it when the walls are cut up.
Subtract big openings, leave small ones
Garage doors, sliding glass doors, and picture windows are large enough that ignoring them inflates your order. Subtract those. Small windows are commonly left in the gross area on purpose, because the offcuts around them feed back into the waste cushion. When unsure, subtract only openings larger than a typical entry door.
Squares are coverage, not boxes
This tool gives you squares and square feet, because that's the unit siding is measured in. How many boxes or bundles that takes depends on the product: coverage per box varies widely by profile and brand. Take your square count to the spec sheet for the exact product to convert it into boxes — don't assume a fixed boxes-per-square number.
Order a little extra — and mind the dye lot
The calculator rounds squares up so you're never short, and keeping an offcut or a spare box for future repairs is cheap insurance. Color can also shift slightly between manufacturing runs, so ordering enough in one go — and noting the dye lot — avoids a visible mismatch if you have to patch a wall later.
Where to buy
Got your numbers? Here's where to pick up what you need:
The terms behind the calculator, in plain English. These are background definitions,
not installation specifications — follow the manufacturer's instructions and your
local building code for the real thing.
Square
The standard unit for measuring and ordering siding — 100 square feet of finished wall coverage. It's the same unit used for roofing. Your total wall area, after waste, divided by 100, is your square count.
Gross wall area
The total area of every wall you're covering, before any openings are removed — either entered directly or summed from each wall's section (length × height).
Net wall area
The gross area minus the big openings you subtract. This is the actual wall surface the siding has to cover, before the waste cushion is added.
Waste factor
The extra material bought above the net area — typically 10 to 15% — to cover cuts around corners and openings, the overlap of lap courses, and the occasional miscut. It's a cushion, not an exact figure.
Wall section
One rectangular piece of wall, measured as length times height in feet. Most houses break cleanly into a handful of sections; gable triangles are roughly width times height divided by two. This calculator accepts up to four sections.
Opening
A door or window cut out of the wall. Large openings — garage doors, sliding doors, picture windows — are worth subtracting; small windows are often left in to feed the waste cushion.
Coverage
How much wall a given box, bundle, or panel of siding covers, stated by the manufacturer and varying by product and profile. Because it isn't fixed, this calculator reports squares and square feet and leaves the box count to the product's spec sheet.
Lap siding
Horizontal boards or panels installed in overlapping courses — including fiber cement, wood, and engineered wood lap. The overlap and corner cuts tend to waste a bit more material than interlocking vinyl, which is why a 15% waste factor is common for lap.
Frequently asked
Add up the area of every wall in square feet, subtract the big openings, then add a waste factor of about 10 to 15%. Divide that total by 100 to get squares, since one square covers 100 sq ft, and round up. For example, 1,000 sq ft of net wall at 10% waste is 1,000 × 1.10 / 100 = 11.0 squares, so you'd order 11. Always confirm the per-box coverage of the product you buy with the manufacturer. Try it in the calculator.
A square is the standard unit for measuring and ordering siding, equal to 100 square feet of finished wall coverage — the same unit used for roofing. Manufacturers sell vinyl, fiber cement, and other siding in boxes or bundles that each cover a fraction of a square, so knowing your total in squares lets you work out how many boxes to buy once you know the per-box coverage.
About 10% is a reasonable default for a simple, mostly rectangular house. Step up to roughly 15% for lap siding, which generates more offcuts, or for a house with many corners, gables, dormers, and angled cuts. Steep gables and lots of trim around windows increase waste because more pieces must be cut to fit. This calculator uses 10% by default and lets you change it.
Subtract the large openings and usually leave the small ones in. Big openings like a garage door, sliding glass doors, or a picture window are large enough that ignoring them inflates your order. Small windows are often left in the gross area on purpose, because the offcuts around them feed back into the waste cushion. When in doubt, subtract only the openings larger than a typical entry door and let the waste factor cover the rest.
Measure the length and height of each wall in feet and multiply them for that wall's area, then add the walls together. For a simple house, treat each side as a rectangle. For a gable end, the triangular section above the wall plate is roughly its width times its height divided by two. This calculator lets you enter up to four wall sections, or you can total everything yourself and enter one number.
It depends entirely on the product and profile, so there's no single answer. Many vinyl boxes cover about two squares, some cover one, and fiber cement and specialty profiles vary widely. Because coverage per box is set by the manufacturer, this calculator gives you the total in squares and square feet and stops there. Take your square count to the product spec sheet to convert it into boxes or bundles.
The wall area you cover is the same either way, but the waste differs. Lap siding — including fiber cement and wood lap — is installed in overlapping horizontal courses and tends to produce more offcuts at corners and openings, so a 15% waste factor is common. Vinyl panels interlock and can waste a bit less on a simple wall, closer to 10%. Either way the coverage is sold in squares of 100 sq ft, and you confirm the exposure and per-box coverage with the manufacturer.
There are 100 square feet in one square. It's a flat coverage unit, not a volume, so a square of siding covers a 10 ft by 10 ft patch of wall — or any other shape adding up to 100 sq ft. Dividing your total wall area, after waste, by 100 gives the squares to order.