Siding Calculator
Siding squares for a house — walls plus gables, minus doors and windows — with vinyl boxes or fiber cement planks, J-channel, corners and starter.
Your estimate
14.22 squares
Siding squares (incl. 10% waste)
- Boxes to buy
- 8
- Net wall area
- 1,293 sq ft
- Walls / gables / openings
- 1,260 sq ft / 225 sq ft / −192 sq ft
- J-channel
- 261 ft (21 pcs)
Show the math
- Walls = 2 × (L + W) × height = 1,260 sq ft
- Gables = 2 × ½ × width × (width ÷ 2 × pitch ÷ 12) = 225 sq ft
- Openings = 2 × 21 + 10 × 15 sq ft = 192 sq ft → net 1,293 sq ft
- × (1 + 10%) = 1,422 sq ft = 14.22 squares → 8 boxes
Shopping list & cost
| Item | Spec | Qty | Cost |
|---|---|---|---|
| Siding | Vinyl siding (double 4 in or 5 in), 2 squares per box | 8 boxes | — |
| Starter strip | 12 ft pieces around the base | 12 | — |
| Outside corner posts | 10 ft pieces | 4 | — |
| J-channel | 12.5 ft pieces — windows, doors, gable rakes | 21 | — |
| House wrap (WRB) | 9 × 100 ft roll = 900 sq ft | 2 roll(s) | — |
Prices are what you enter under Advanced options. Estimates only — check stock and pricing with your supplier.
Quick answer A 40 × 30 ft house with 9 ft walls, two 6/12 gables, 2 doors and 10 windows has 1,293 sq ft of net wall area — 14.22 squares with 10% waste, or 8 boxes of vinyl siding at 2 squares per box, plus 21 pieces of J-channel. A 12 × 9 m house needs about 13.71 squares. Siding = 2 × (L + W) × H + gables − openings.
Method & assumptions
Walls = 2 × (Length + Width) × Height Gable = ½ × Width × (Width ÷ 2 × pitch ÷ 12), per gable Net = Walls + Gables − (Doors × 21 + Windows × 15 sq ft) Squares = Net × (1 + waste %) ÷ 100
- Square
- 100 sq ft of wall
- Exposure
- visible height of each course of lap siding
- Vinyl box
- typically 2 squares (200 sq ft) — check the carton
Assumptions & limits
- A rectangular house; add bump-outs, dormers and garages separately.
- Soffit and fascia are not included.
- Fiber cement at 7 in exposure on 12 ft planks (7 sq ft each); engineered wood 16 ft at 6.83 in.
- Trim lengths are typical: starter 12 ft, outside corners 10 ft, J-channel 12.5 ft.
Rounding: purchase quantities are always rounded up to whole units as sold. See our methodology.
Diagram
How to use this calculator
- Measure the house length and width at the walls, and the wall height from the bottom of the siding to the eaves.
- Count the gable ends and enter the roof pitch — the gable triangle is calculated for you.
- Count doors and windows. Typical sizes are subtracted (21 and 15 sq ft); measure unusual openings separately.
- Choose the siding product and keep 10% waste (15% for complex walls).
- Use the trim list as a starting point and adjust after walking the house.
Worked examples
Imperial: 50 × 26 ft ranch, 8 ft walls, 2 gables at 5/12, 3 doors, 12 windows
- Walls = 2 × 76 × 8 = 1,216 sq ft
- Gables = 2 × ½ × 26 × 5.42 = 141 sq ft
- Net = 1,357 − 63 − 180 = 1,114; +10% = 1,225 sq ft = 12.25 squares → 7 boxes
Fiber cement on the same house
- 1,225.2 sq ft ÷ 7 sq ft per plank = 175.03 → 176 planks
- (8¼ in planks at 7 in exposure: 14.3 planks per square)
In depth: siding planning notes
Measuring walls, gables and openings
Walk around the house and break it into simple shapes. The rectangular walls are the perimeter times the wall height, measured from the bottom of the siding to the soffit. Gable ends add a triangle above the wall on each end with a pitched roof: half the width times the gable height, where the gable height is half the width times the pitch ÷ 12. A 30 ft wide gable at 6/12 is 7.5 ft high and 112.5 sq ft — easy to forget and a common reason for running short.
Subtract doors and windows, but don't expect every square foot back: the pieces cut out around openings are rarely long enough to reuse, which is why the waste factor stays at 10% even after subtracting them. Garage doors, bay windows and sliding doors are much bigger than the typical 15 and 21 sq ft used here — measure those and subtract the difference. Bump-outs, dormers and porches are best calculated as separate small walls.
Trim and accessories
Siding needs a system of trim to look finished and keep water out. Starter strip runs around the base of the walls; outside corner posts cover each external corner (and inside corners need their own pieces); J-channel frames windows and doors, runs along gable rakes and catches siding under soffits. Undersill trim holds the cut edge of panels beneath windows. The calculator gives a first count from the house dimensions, which is usually within a few pieces — walk the house with the list before ordering.
Behind the siding, a water-resistive barrier such as house wrap is required by code, with window and door openings flashed before the siding goes on. Vinyl must be nailed loosely in the center of the slots so it can expand and contract; fiber cement is face- or blind-nailed to manufacturer spacing and needs clearance from the ground and roofs. Coverage per box or plank varies by product and exposure, so check the label and adjust the calculation if your product differs.
Reference table
| Situation | Extra |
|---|---|
| Simple box house, few openings | 10% |
| Many windows, gables or corners | 12–15% |
| Dormers, bump-outs, multi-story | 15–20% |
Key facts
- 1 square
- 100 sq ft
- Vinyl box
- ≈ 2 squares
- 8¼ in fiber cement, 7 in exposure
- 7 sq ft per 12 ft plank
Tips & common mistakes
- Install a water-resistive barrier (house wrap) and flash windows before siding — siding sheds most water, the WRB handles the rest.
- Vinyl siding must hang loose: nail in the center of the slots and leave about 1/32 in so panels can move.
- Keep fiber cement 6 in above grade and 1–2 in above roofs per manufacturer instructions.
- Buy all siding from one lot to avoid color shifts.
Frequently asked questions
How many squares of siding do I need?
Add up wall area plus gables, subtract openings, add 10% and divide by 100. A typical 1,500 sq ft single-story house needs roughly 14–16 squares.
How many boxes of vinyl siding per square?
Most vinyl siding cartons contain 2 squares (200 sq ft), so you need half a box per square.
Should I subtract windows and doors from siding?
Yes for large openings. Pros subtract windows and doors but keep the waste factor, because cut-offs around openings are rarely reusable.
How much J-channel do I need?
Around every window and door (roughly 16–17 ft each), along gable rakes and where siding meets the soffit or roof.
How do you calculate gable siding?
A gable is a triangle: ½ × base × height. Height = half the width × pitch ÷ 12 — a 30 ft wide 6/12 gable is 7.5 ft high and 112.5 sq ft.
Sources
- James Hardie – National Product Catalog (PDF) — accessed : “HardiePlank® Lap Siding: 7.25 in. (6 in. exposure) and 8.25 in. (7 in. exposure) widths; 12 ft. length”
- CertainTeed – 2020 Siding Product Catalog, Encore vinyl siding (p. 25, distributor-hosted) — accessed : “DOUBLE 4" CLAPBOARD … Panels/Ctn.: 24 · Squares/Ctn.: 2”
- Vinyl Siding Institute – Vinyl Siding Installation Manual — general reference — not cited for a specific figure
- ICC – 2021 IRC R703 exterior covering — general reference — not cited for a specific figure
Default values (yields, coverage rates and densities) are typical figures from manufacturer literature. Always check the label on the product you buy.
Related calculators
- Roofing CalculatorRoof area from building size, overhang and pitch for gable, hip or shed roofs — squares, shingles, underlayment, drip edge, ice shield and ridge cap.
- Square Footage CalculatorFind the area of a room or yard in square feet, square meters and square yards — rectangles, triangles, circles and trapezoids.
- Roof Pitch CalculatorConvert rise and run or an angle into roof pitch (x/12), degrees, percent slope and the pitch factor — plus ridge height and rafter length.
Learn more in our guides
Method, waste and worked examples: Roof area, squares and waste.
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DIYCalcLab. “Siding Calculator.” Oct 19, 2026. https://diycalclab.com/roofing/siding-calculator/
Estimates only. Verify quantities with your supplier and local building codes. For structural, electrical or safety-critical work, consult a licensed professional. Full disclaimer.