Siding Calculator
Find out how many squares of siding to order for your house — the unit siding is actually sold and quoted in.
House dimensions
Results
For a 40 ft × 30 ft house with 9 ft eave walls, 2 doors, and 8 windows, at 10% waste, you'll need about 13 squares of siding.
Siding needed
13 squares (1 square = 100 sq ft)
That's a typical order for a single-story to modest two-story house.
Most vinyl ships two squares per carton, so confirm carton coverage before ordering — an odd-square result may round up to the next carton. Remember accessories (starter strip, J-channel, corner posts) are a separate linear-foot order.
Net wall area (after openings): 1103 sq ft
Area to order (incl. waste): 1213 sq ft
Gable triangles above eave height are not included — see "How this works" below for the simple addition to make for gables.
How this works
Wall area is modeled as the house's perimeter times its eave height: 2 × (length + width) × height. For each door and window you enter, a standard exterior opening is subtracted — about 20 sq ft per door (0.9 m × 2.1 m) and 15 sq ft per window (0.9 m × 1.5 m). These are disclosed structural assumptions, used instead of asking you to measure every opening; if your house has unusually large openings (a garage door, a picture window), subtract those manually. The net area is then inflated by your selected waste factor — 10% for simple rectangular layouts, 15% for complex layouts with gables, dormers, or many corners, matching the convention in vinyl siding industry guidance and retailer estimators — and divided by 100 sq ft to express the result in squares, the trade unit siding is ordered and priced in. The squares figure is rounded up to a whole square, since partial squares aren't purchasable in practice (and most vinyl ships in two-square cartons, which may round you up further at the counter). Two disclosed limitations: gable triangles above eave height are not modeled (compute ½ × width × rise per gable and add it — see the FAQ), and accessories (starter strip, J-channel, corner posts) are a linear-foot takeoff excluded from area math entirely. The unit toggle switches inputs and outputs between imperial and metric; internally every calculation runs in canonical SI units, so switching never introduces rounding drift Siding "square" convention and waste guidance: Vinyl Siding Institute installation manual; 10–15% waste per retailer siding estimators (e.g. Lowe's).
Worked example
A 40 ft × 30 ft single-story house with 9 ft eave walls, 2 exterior doors, and 8 windows, simple layout (10% waste): gross wall area is 2 × (40 + 30) × 9 = 1,260 sq ft. Subtracting 2 doors (≈ 20 sq ft each) and 8 windows (≈ 15 sq ft each) leaves about 1,103 sq ft of sided wall. Adding 10% waste gives roughly 1,213 sq ft — 12.13 squares, rounded up to 13 squares to order. At the common two-squares-per-carton packaging, that's 7 cartons.
A second example: a two-story colonial with gables
A 36 ft × 28 ft two-story house with 18 ft eave walls, 3 doors, and 14 windows, complex layout (15% waste): gross wall = 2 × (36 + 28) × 18 = 2,304 sq ft; openings remove about 61 + 210 = 271 sq ft, leaving ≈ 2,033 sq ft; × 1.15 ≈ 2,338 sq ft = 23.4 squares → 24 squares from the calculator. Then add the gables by hand: two gable ends 28 ft wide with a 7 ft rise are 2 × (½ × 28 × 7) = 196 sq ft; with 15% waste that's another 225 sq ft ≈ 2.3 squares. Total order: about 26–27 squares. Skipping the manual gable step — the single most common siding-estimate omission — would have left this job more than two squares short.
Common mistakes
Forgetting the gables
The perimeter × eave-height model covers the rectangular wall band only. Gable triangles routinely add 2–3 squares on a typical house — enough to run genuinely short mid-job. Compute each gable's area (½ × width × rise) and fold it in before ordering; see the gable FAQ above for the method.
Skipping the opening subtraction on window-heavy houses
On a house with 12+ windows, openings remove well over a full square of area. If you estimate gross wall area and also add 10–15% waste on top, you double-pad the order. This calculator subtracts standard opening sizes so the waste factor covers only genuine cutting waste.
Ordering field panels and forgetting accessories
Starter strip, J-channel, corner posts, and utility trim are separate line items ordered by the linear foot, and a job stalls just as hard from running out of J-channel as from running out of panels. Walk the house and measure: base perimeter for starter, opening perimeters and rake lengths for J-channel, one post per corner.
Using 10% waste on a complex layout
Dormers, bays, and multiple gables generate short angled offcuts that rarely reuse. The industry convention — reflected in this calculator's selector — is 15% for complex layouts. Choosing 10% to make the order cheaper is the most common way DIY siding orders come up a square short.
Mixing manufacturing lots
Buying 10 squares now and 2 more next month risks a visible color shift between lots, especially on large uninterrupted walls. Order the full calculated quantity at once and check that carton lot numbers match.
Measuring wall height to the peak instead of the eave
Entering peak height inflates all four walls' area even though only the two gable-end walls carry the triangle — on a two-story house with a steep roof this can overstate the order by 20% or more. Enter eave height and handle gables as a separate addition.
Confusing squares with square feet at the counter
A "13-square" order is 1,300 sq ft. It sounds obvious, but mixed-unit conversations with suppliers ("I need thirteen") have produced both 13-carton and 13-sq-ft misorders. State the unit explicitly: 13 squares, about 7 two-square cartons.
When this calculator's model stops applying
- Houses that aren't rectangular in plan (L-shapes, T-shapes, additions): perimeter × height still works if you use the true total perimeter of the exterior walls — measure each wall segment and sum, rather than entering the bounding rectangle's length and width, which understates the perimeter of any non-convex footprint.
- Steep-roofed or story-and-a-half homes (Cape Cods, A-frames): the gable and dormer area can rival the rectangular wall band itself. Compute those areas explicitly rather than trusting a waste bump; an A-frame is nearly all gable and this model does not fit it.
- Partial re-siding of one elevation: run the calculator with that wall's length as the perimeter contribution (enter its length and width so 2 × (L + W) × H equals the target area is NOT valid) — instead measure the single wall's area directly (length × height, minus its openings, plus its gable) and divide by 100 for squares. The whole-house model exists for whole-house orders.
- Non-standard opening sizes: a garage door (≈ 112 sq ft for a 16×7) is not a standard door — subtract it manually rather than counting it as one door, or the order will run about a square heavy.
- Board-and-batten and vertical siding: area math holds, but waste behaves differently (vertical panels cut to wall height leave one offcut per panel, tied to your specific wall height vs. panel length), so the 10/15% convention may under- or overshoot; compute panel counts from your product's coverage width instead.
- Metric-market panels: profiles sold in metric lengths/exposures don't map cleanly onto the 100-sq-ft square. Use the calculator's m² output and your panel's per-piece coverage in m² directly.
- Insulated vinyl siding and thick fiber cement: the coverage math is unchanged, but carton coverage per square differs and per-piece weight changes handling waste; verify carton coverage before converting squares to cartons.
- Historic or masonry-clad walls being partially sided: subtracting non-sided areas (brick chimney chases, stone wainscot bands) has to be done by hand — measure and subtract those areas from the calculator's order area before dividing into squares.
FAQ
What is a siding "square"?
A square is the siding trade's ordering unit: 1 square = 100 square feet of wall coverage. Vinyl siding cartons, contractor quotes, and retailer pricing are all expressed in squares, which is why this calculator's primary result is squares rather than square feet — you can hand the number directly to a supplier. A typical single-story ranch house runs 10–15 squares; a two-story colonial commonly runs 20–30.
Why does the calculator subtract doors and windows?
Siding doesn't cover openings, so each door and window you enter removes a standard opening's worth of area: about 20 sq ft (0.9 m × 2.1 m) per exterior door and about 15 sq ft (0.9 m × 1.5 m) per window. Some estimators skip this subtraction and treat openings as extra waste allowance — that's defensible for a house with few, small windows, but on a window-heavy wall it can overstate the order by a full square or more, so this tool subtracts them and adds waste explicitly instead.
Should I choose 10% or 15% waste?
Choose 10% for a simple rectangular footprint with straight eaves and few corners. Choose 15% when the layout is complex: multiple gables, dormers, bay windows, angled walls, or many inside/outside corners. Gable-end triangles and angled cuts generate offcuts that often can't be reused, and each additional corner adds trimmed panel ends — the 10%/15% split is the convention used across vinyl siding industry guidance and retailer estimators.
Does this calculator handle gable ends?
Not automatically — it models walls as perimeter × height (foundation to eave). For each gable triangle, compute its area separately (½ × gable width × gable rise) and add it by temporarily increasing the wall height: dividing total gable area by the house perimeter gives the equivalent extra height to enter. A pair of typical gables on a 30-ft-wide house with a 6/12 roof pitch adds about 225 sq ft — 2.25 squares — so gables are not a rounding error you can ignore.
Does the result include trim, starter strip, J-channel, and corner posts?
No — squares cover field panels only. Accessories are ordered by linear footage: starter strip along the base (≈ house perimeter), J-channel around every opening and along gable rakes, corner posts per outside/inside corner, and utility trim under windows. A rough rule of thumb is that accessories add 10–20% to the panel cost, but they're a linear-foot takeoff, not an area calculation, so this tool intentionally leaves them out rather than guessing.
Does this work for fiber cement, engineered wood, or wood lap siding?
The wall-area and waste math is material-independent, and fiber cement is also commonly quoted in squares — so yes for estimating coverage area. But per-material ordering differs: fiber cement planks and engineered wood are sold in pieces of specific exposure (e.g. a 8-1/4 in plank with 7 in exposure covers 7 in × 12 ft per piece), so convert the ordered area to piece counts using your product's stated exposure, not its nominal width.
Why does my contractor's estimate differ from this one?
Contractors typically measure each elevation (wall face) separately, include gables explicitly, count accessories, and apply their own waste factor based on crew habits and the specific panel profile's reusability of offcuts. If a professional quote is more than about 15% above this calculator's result plus your gable math, ask for the elevation-by-elevation takeoff — the discrepancy is usually gables, a steep waste factor, or accessories folded into the square count.
Should I order everything at once?
Yes, and from the same production run where possible. Vinyl siding color varies subtly between manufacturing lots, and a wall mixing lots can show banding in low-angle light. Ordering the full quantity (including waste) at once, with matching lot numbers on the cartons, is the same batch-matching discipline used for paint — and a reason to round up rather than plan a second trip.
How many squares are in a typical carton of vinyl siding?
Most vinyl siding is packaged two squares per carton (some profiles are 1 or 1.5). If your result is an odd number of squares, you may effectively round up to the next whole carton at purchase — check your product's carton coverage before assuming you can buy exactly the calculated number of squares.
Do I measure height to the eave or to the roof peak?
To the eave — the height where the wall meets the roofline, typically about 9 ft for a single story and 18–19 ft for two stories. The triangle above eave height on gable-end walls is the gable area, handled separately (see the gable FAQ above). Measuring to the peak on all four walls would double-count area the roof covers on the non-gable sides.
Can I switch between imperial and metric partway through?
Yes — the unit toggle converts every field you've already entered, and results switch between squares/sq ft and m². Internally the tool always computes from the same canonical values regardless of the displayed unit, so switching doesn't introduce rounding error. Note that the square remains a 100-sq-ft unit by definition even in metric display (9.29 m²).
Does old siding removal change the amount I need?
Not the amount — the wall is the same size — but it changes what else you buy. Going over existing flat surfaces may need furring and will need longer fasteners; a tear-off usually reveals sheathing repairs and requires new house wrap over the whole calculated wall area, which conveniently equals this calculator's gross-area figure before opening subtraction.
Related tools
Paint Calculatorif you're painting instead of (or before) re-siding, estimate how many gallons of paint the same walls need — the area math starts from the same house dimensions.More exterior tools (siding accessories and house-wrap estimators) are planned but not yet published.