Enter your wall sizes - gable ends included - take off the doors and windows, and get the net wall area in square feet, the number of siding squares, and the boxes of vinyl to buy, or the fibre-cement (Hardie) and lap boards by their exposure, plus the J-channel and corner-post lengths. Works in feet or metres.
Gross wall area: 288 sq ft
A standard carton is about 200 sq ft (2 squares).
Net area: 256 sq ft · 2.56 squares
J-channel also wraps every door and window perimeter you entered above.
Net wall area
256 sq ft
Siding squares
2.56
Gross area
288 sq ft
Trim is sold in fixed sticks, so round the J-channel and corner-post runs up to whole lengths.
Siding clads the outside walls, so the job starts like a paint or drywall estimate: a gross wall area (each wall’s length times height), with the doors and windows taken off to leave the net area you actually cover. From there the two common products are bought differently - vinyl by the square and the box, lap boards by their exposure:
gross wall area = sum of (wall length × wall height)
net area = gross − (door & window areas)
squares = net area (sq ft) ÷ 100
vinyl boxes = ceil( net area × wastage ÷ box coverage ) (carton ≈ 2 squares)
lap board run = net area ÷ exposure → boards = ceil( run × wastage ÷ board length )
J-channel = perimeter of every opening + eave / soffit run
corner posts = outside corners × wall height
A square is 100 sq ft of finished wall - the same trade unit roofers use - and vinyl is normally boxed two squares to the carton. Lap boards (vinyl, fibre-cement or timber) overlap, so a board only covers its exposure, the visible reveal of each course; the lineal run you need is the net area divided by that exposure. The trim is sized off the geometry, not the field area: J-channel wraps every opening and runs the eaves, and corner posts run the wall height at each outside corner.
This example follows the unit system you pick in the calculator above.
Four 32 ft × 9 ft walls clad in vinyl, less two 4 ft × 4 ft windows, 10% wastage:
The profile sets the exposure - the height each course covers - which is what turns a wall area into a panel count. These are the everyday horizontal profiles:
| Profile | Exposure | Notes |
|---|---|---|
| Double 4 (D4) | 8 in / 200 mm (two 4 in courses) | The default clapboard look |
| Double 4.5 (D4.5) | 9 in / 230 mm | Slightly taller courses |
| Double 5 (D5) | 10 in / 250 mm | Fewer courses, faster to hang |
| Single 8 / Dutch lap | 8 in / 200 mm | One wide plank or a Dutch-lap shadow line |
| Board & batten (vertical) | 7 in / 180 mm net per panel | Vertical look, sold the same way by the square |
A box of vinyl covers about 2 squares (200 sq ft) whatever the profile - the profile changes the panel count in the box, not the wall area it covers - so the calculator works in net area and squares and lets you set the coverage per box.
In the United States, exterior wall cladding is called siding - vinyl, fibre-cement (such as James Hardie) or wood lap (clapboard), and it is bought by the "square" of 100 sq ft, with vinyl boxed two squares (about 200 sq ft) to the carton. A lap panel covers only its exposure - the visible reveal, commonly 8 in on a "double 4" profile - so the panel count comes off the net wall area, not the gross. Set the siding type and the box coverage or board exposure in the calculator above to match what your supplier stocks, so the count comes out right.
For the recognised specification and fixing detail, see ASTM D3679, the rigid PVC siding specification, installed to ASTM D4756 and the Vinyl Siding Institute (VSI) program.
Add up each wall as length times height for the gross area, subtract the doors and windows to get the net area, then divide by 100 sq ft to get the number of siding squares. For vinyl, multiply the net area by your waste allowance and divide by the carton coverage (a box is usually 2 squares, about 200 sq ft) to get the boxes. The calculator does every step and rounds up to whole boxes or boards.
A "square" is 100 sq ft of finished wall, and vinyl siding is almost always boxed two squares - about 200 sq ft - to the carton, so one box covers roughly two squares. A square of standard siding works out to around 10 to 12 panels depending on the profile. Set the coverage per box in the calculator if your product is boxed by the single square instead.
A square is the roofing-and-siding trade unit of 100 square feet of coverage - it has nothing to do with a square shape. It is the same unit roofers use for shingles, so a 1,000 sq ft wall is 10 squares. Pricing, coverage and order quantities are all quoted in squares in the US and Canada, which is why the calculator shows squares alongside the boxes.
Lap boards overlap, so only the exposure - the visible reveal of each course - actually covers wall. A board therefore covers its exposure times its length, and the lineal run you need is the net wall area divided by the exposure. Divide that run by the board length and round up for the number of boards. Pick "Lap board" in the calculator and enter your exposure and board length to get the piece count.
Fibre-cement lap siding like James Hardie HardiePlank is estimated by its exposure, exactly like wood lap. Take the net wall area, divide by the exposure (HardiePlank is commonly run at a 6 in or 7 in exposure depending on the board width), then divide by the board length - Hardie planks are 12 ft - and round up. Pick "Lap board" in the calculator and set the exposure and the 12 ft board length; it gives the piece count with waste added.
A gable end is a triangle, so its area is half the base times the height to the peak. In the calculator, add the wall and switch its shape to "Gable / triangle", then enter the gable width as the base and the height from the eave line up to the ridge. For a wall with a gable on top, enter the rectangle below the eave as one wall and the triangle above as another, and the calculator adds them.
A 10 ft × 12 ft shed with 8 ft walls has four walls totalling about 352 sq ft of gross area (two at 10×8 and two at 12×8), before the door and any window come off and before the gable ends are added. That is roughly 3.5 squares, so about 2 boxes of vinyl at two squares a box with waste. Enter each wall, take off the door, add the gable triangles, and the calculator gives the exact figure - see the how much siding do I need guide for more shed and house sizes.
Yes. Metal panel siding is sold by the square the same way as vinyl, so use the vinyl mode and set the coverage per box or panel. LP SmartSide and other engineered-wood lap boards are estimated by their exposure like fibre-cement, so use the lap mode with the board exposure and length. The wall-area and trim maths are the same whatever the material; only the way it is packaged changes.
J-channel runs around the perimeter of every door and window so the siding ends are tucked in, plus along the eaves and soffits, so add up those runs. Corner posts run the full height of the wall at each outside corner, so multiply the number of corners by the wall height. The calculator works the J-channel out from the openings you enter (plus any eave run) and the corner posts from the corner count and height - round each up to whole sticks when you order.
Yes - subtract the area of each door and window from the gross wall area, because you are not cladding over them. The calculator deducts every opening you add. It is common to keep a small allowance by not deducting very small openings, but for a tight estimate take them all off and let the waste percentage cover the offcuts around them.
Allow about 10% for a simple gable wall and 15% where there are lots of openings, corners and short courses that force more cutting. Steep gable ends and dormers push it higher. It is safer to round up - a later batch of vinyl can vary slightly in shade - so the calculator adds your chosen waste allowance before rounding up to whole boxes or boards.
What vinyl, fiber cement and James Hardie siding cost, and how to price your own wall area by the square.
Read guide→Turn wall square footage into squares and boxes of vinyl or lap boards.
Read guide→Upfront cost, maintenance, lifespan, fire and looks compared.
Read guide→Break the walls into shapes, subtract openings, total into squares.
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