Work out how much siding you need with our free calculator. Get squares, piece counts, starter strip, J-channel, corner trim, and a full cost breakdown.
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Every siding job starts with one number: the net wall area you actually have to cover. Get that wrong and you’re either short on material mid-install or you’ve overpaid for boards that sit in the garage. This calculator handles the arithmetic in one pass. Feed it your building length, width, eave height, and opening sizes. It computes gross area, deducts doors and windows, converts to squares, applies your waste factor, and returns piece count plus every trim and accessory length you need. Gable ends get their own mode so you’re not guessing at triangle area. Cost fields stay separate from dimensions, so you can build a bid without re-entering wall sizes. Metric and imperial both work, and the whole thing runs in your browser.
Set your unit system. Imperial uses inches, feet, and square feet. Metric uses millimeters, meters, and square meters.
Pick a wall input mode. Single Wall handles one face. Perimeter covers a whole building. Gable End adds a triangle on top of a rectangle. Direct Area Entry skips geometry if you already know the square footage.
Enter the wall dimensions for your chosen mode. For gable, add the peak height above the eave.
Subtract openings. Enter door count, width, and height. Do the same for windows.
Choose a siding preset or enter custom exposure and piece length. The exposure field drives piece count, not nominal board width.
Set your waste factor. Default is 10%.
Toggle trim and accessories. Starter strip, corner trim, J-channel, house wrap, and frieze trim each have their own switch.
Enter unit costs and read the summary. The result panel shows squares, pieces, linear feet, and total cost.
The tool works in four stages: gross area, net area, squares, then pieces. Gross area depends on your input mode. A single wall is length times height. A perimeter is building perimeter times eave height. A gable adds a triangle (half the width times peak height) on top of the rectangle. Direct entry skips all of that.
Formula: Gross Area = Wall Length × Wall Height
Formula: Gable Area = (Width × Eave Height) + (0.5 × Width × Peak Height)
Formula: Net Area = Gross Area − (Doors × Door W × Door H) − (Windows × Window W × Window H)
Formula: Area with Waste = Net Area × (1 + Waste % ÷ 100)
Formula: Squares = Area ÷ 100 ft² (imperial) or ÷ 9.29 m² (metric)
Formula: Pieces = Ceiling(Area with Waste ÷ (Exposure × Piece Length))
Squares are a roofer’s unit, but siding suppliers use them too. One square equals 100 square feet. A 10-square job means 1,000 square feet of coverage. Vinyl, fiber cement, and engineered wood all get priced per square at the supplier level.
Piece count uses the exposed face of the board, not the nominal width. A 5-inch vinyl lap board has a 5-inch exposure in this tool’s default. Multiply exposure by piece length and you get the coverage per piece. For a 12-foot piece at 5-inch exposure, that’s 5 square feet per piece. Divide area with waste by that number and round up.
Trim calculations are simpler. Starter strip runs along the bottom perimeter. Corner trim runs the full height at each corner. J-channel runs around every opening plus a rough allowance along vertical terminations. House wrap covers net area plus 10%. Frieze trim runs along the top perimeter if you enable it.
A 36-foot by 28-foot building, 9-foot eave height, all four sides. Three doors at 3×7 and six windows at 3×4. Vinyl lap siding, 5-inch exposure, 12-foot pieces, 10% waste.
Step 1 — Perimeter. 2 × (36 + 28) = 128 ft.
Step 2 — Gross area. 128 × 9 = 1,152 ft².
Step 3 — Openings. Doors: 3 × 3 × 7 = 63 ft². Windows: 6 × 3 × 4 = 72 ft². Total = 135 ft².
Step 4 — Net area. 1,152 − 135 = 1,017 ft².
Step 5 — Squares. 1,017 ÷ 100 = 10.17 squares net.
Step 6 — Waste. 1,017 × 1.10 = 1,118.7 ft², or 11.19 squares with waste.
Step 7 — Pieces. Piece area = 5 in ÷ 12 × 12 ft = 5 ft². Pieces = ceil(1,118.7 ÷ 5) = 224 pieces.
Step 8 — Total siding length. 224 × 12 = 2,688 ft.
Step 9 — Trim. Starter = 128 ft. Corner trim = 4 corners × 9 ft = 36 ft. J-channel = opening perimeter (3×2×10 + 6×2×7 = 144 ft) + 0.5 × 128 = 208 ft. House wrap = 1,017 × 1.10 = 1,118.7 ft².
Step 10 — Cost at $180 per square, $1.20/ft starter, $2.50/ft corner, $1.10/ft J-channel, $0.12/ft² wrap.** Siding = 11.19 × 180 = $2,014.20. Starter = $153.60. Corner = $90.00. J-channel = $228.80. Wrap = $134.24. Material subtotal = $2,620.84.
Interpretation: Order 224 pieces of 12-foot vinyl lap. That’s 11.19 squares. Add trim and wrap and you’re around $2,600 in materials before labor. The tool rounds up per piece, so you’ve got a small buffer on top of the 10% waste.
Multiply wall length by height for each face, add them up, subtract openings, then divide by 100 for squares. Add your waste percentage. A 1,017-square-foot wall with 10% waste becomes 11.19 squares. Order the next full square up.
It depends on the exposure and piece length. A square is 100 square feet. With 5-inch exposure and 12-foot pieces, each piece covers 5 square feet, so one square takes 20 pieces. Wider exposure or longer pieces mean fewer pieces per square.
Vinyl runs $3 to $7 per square foot installed. Fiber cement is $6 to $12. Engineered wood sits around $5 to $9. The material itself is usually 40% to 60% of the installed number. The calculator’s cost-per-square-foot output uses whatever unit prices you enter.
Most vinyl lap siding has a 4-inch or 5-inch exposure. Double 4 and double 5 profiles show two boards in one panel. The preset dropdown includes 4-inch, 5-inch, and double 5 options. Check the product spec sheet if you’re using an unusual profile.
Yes. The preset list includes fiber cement lap at 7-inch and 8.25-inch exposure, plus a 4×8 panel option. Enter the fiber cement cost per square and the tool handles the rest.
Measure the width at the base, the eave height from ground to where the roof meets the wall, and the peak height above that line. The calculator adds the rectangle and the triangle for you. Do this for each gable end separately if the dimensions differ.
Yes. Siding doesn’t cover openings, so any full-height door or window reduces the net wall area. The tool deducts them by count times width times height. A single 3×7 door removes 21 square feet. Six windows at 3×4 remove 72 square feet.
Standard trim includes starter strip along the bottom, corner trim at every outside corner, J-channel around openings, and frieze or top trim if you have a rake or soffit line. The calculator gives you a length for each.
Yes. It runs in your browser, there’s no signup, and you can use it as many times as you want. Nothing gets stored on a server.
The tool uses opening perimeter plus half the wall perimeter as a rough approximation. It doesn’t map every vertical termination or trim joint. For a precise takeoff, measure the actual runs where J-channel will sit and add them by hand.
Board and batten typically uses a 12-inch to 16-inch exposure depending on the batten width and design. The calculator has a 16-inch preset. Enter a custom value if your plan calls for a narrower or wider gap.
Yes. Set wall mode to Single Wall and enter length and height. Leave the number of identical walls at 1. That’s the right mode for an accent wall or a single face.
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