Siding Calculator

How to use the siding calculator

1. Pick your siding: vinyl Double 4″, Double 4.5″ Dutch lap or Double 5″, or a James Hardie HardiePlank width from 5¼″ to 12″.
2. Type the house’s outside length and width, and pick the stories. An L-shaped house: add the two wings’ lengths and count its inside corner.
3. Count the gables (the triangles of wall under the roof’s peak) and pick the roof pitch: a 6/12 roof rises 6 inches every foot.
4. Soffit and fascia instead? Switch What to count: the same house’s eaves, with your soffit panel, the overhangs and where the soffit is vented.
5. Count the windows, outside doors and garage doors. Choose whether the windows and doors come off the wall area or stay in as a waste allowance, and how much extra to buy.
6. Price it installed or for the materials only, and type a contractor’s quote if you have one: the calculator places it in the national range.
7. You get the boxes or planks, the squares, and every starter strip, J-channel, trim piece and corner post. Copy link keeps your house; the green button opens the paint calculator’s outside mode with the same house filled in.

How siding is measured

Siding is sold by the square. The Vinyl Siding Institute’s manual: “Every 100 square feet (9.29 square meters) is called a “square” for ordering purposes.” The calculator measures the house the way the manual and the siding makers’ own estimators do:

1. The walls: the distance round the house times the height from the foundation to the eaves. The calculator takes 10 ft for the first story and 9 ft for each story above it. A 50 × 30 ft house is 160 ft round, so one story is 1,600 sq ft of wall.
2. The gables: a triangle is “½ height × width”. A gable over a 30 ft end under a 6/12 roof rises 7.5 ft (half the width, 15 ft, times 6/12), so it adds ½ × 7.5 × 30 = 112.5 sq ft. Two gables add 225.
3. The openings: the calculator takes 15 sq ft for a window (3 × 5 ft), 20 for a door and 63 for a garage door (9 × 7 ft).
4. The waste: cuts round the windows and the gables’ angles use up siding. Kaycan’s estimator says “Add 10% for waste”.

Take the windows off, or leave them in?

The makers disagree, and both ways are on the calculator. Kaycan’s estimator subtracts every window and door: “These amounts will be subtracted from the total siding requirements.” The Vinyl Siding Institute leaves them in: “Windows and doors are not usually deducted. Including them will provide an allowance factor for waste.” Both take the garage doors off: “If the windows and doors are extremely large (such as a garage or sliding glass doors), some deductions can be made”. Leaving the windows in buys more siding — on the house in the quick answer, 10 boxes instead of 9 — and is the safer choice for a house with many small windows.

Boxes of vinyl siding and HardiePlank planks per square

A plank covers its length times its exposure — the part that shows once the course above laps over it — not its full width. James Hardie’s chart counts the planks “Number of 12′ planks, does not include waste”, so add your waste on top. The calculator also counts 7½″, 8″ and 9½″ planks; the chart counts 9½″ planks as it counts 9¼″ ones (13 a square), and so does the calculator.

The trim and accessories

• Starter strip sets the first course. The manual: “To estimate the amount of starter strip required, measure the linear feet around the entire base of the house.” The calculator leaves out the doors and garage doors, which reach the ground. Vinyl starter comes in 10 ft strips; for HardiePlank, “Starter strips are easily made by ripping 1 1/4-in. pieces of HardiePlank”, so an 8¼″ plank gives 6 strips.
• J-channel (vinyl) runs up the sides and across the top of every window (13 ft for a 3 × 5 ft window), round the sides and head of every door (17 ft) and garage door (23 ft), and up both rakes of every gable. It comes in 12′6″ lengths.
• Finish trim (vinyl) holds the top course under the eaves and the cut course under each window, 12′6″ lengths.
• Corner posts (vinyl): one at every outside corner — a box house has 4, an L-shaped one 5 — and an inside corner post at each inside corner, both 10 ft long; a two-story wall takes two posts lapped.
• HardieTrim boards (fiber cement), 12 ft, for the “frieze, fascia, rake, window, door, and corner details”: two boards make each outside corner, one each inside corner, and boards round every window, door and garage door, under the eaves and up the rakes.
• Nails (vinyl): the manual says to “multiply the total square feet of siding by 0.005 for aluminum nails and 0.01 for roofing nails, staples, and screws”.

Soffit and fascia: the same house, its eaves

Switch What to count to Soffit and fascia and the soffit calculator takes the same house’s length, width, gables and pitch, and three answers about the roof: how far the eaves overhang the wall, how far the roof runs past each gable (the rake), and where the soffit is vented.

• The eaves run under every wall a gable does not take, on past each gable end by the rake’s overhang, and round each corner of a hip roof. The soffit’s area is that length times the overhang; the rakes add their slopes times theirs.
• The pieces. The Vinyl Siding Institute’s manual: “Vinyl soffit is designed to be easily installed lengthwise from wall to fascia.” Each piece is the overhang less ½″: “Then subtract 1/2″ (12.7mm) to allow for expansion.” A 12″ overhang takes 11½″ pieces, 12 from a 12 ft panel, each covering the panel’s width along the eave.
• Vented or solid. Vented panels go where the attic draws its air in, usually under the eaves; the rakes can be solid. The manual says to “use vented soffit or other vented products as required. Refer to manufacturer’s product specific net free area.”
• Fascia covers the board at the roof’s edge, round the eaves and up the rakes, in 12 ft lengths: “When overlapping aluminum/vinyl fascia covers, make sure to overlap 3/4″ (19mm).”
• F-channel runs along the wall under the soffit and holds its inner end, 12′6″ lengths (“You can use accessories such as J-channel or F-channel.”). Back-to-back J-channel joins the soffit where two eaves meet at a corner and at each gable’s peak.
• Over 16″ deep, the soffit needs support across its middle: “Nailing strips must be installed as shown in Figure 64 if the eave span is greater than 16″ (406mm), unless otherwise specified in the soffit manufacturer’s instructions.”

The 50 × 30 ft house above, two gables on a 6/12 roof, 12″ eaves and 12″ rakes, Triple 4″ vinyl soffit. The two 50 ft eaves each run a foot past both gable ends: 104 ft, so 104 sq ft. The four rake slopes are 16.8 ft each: 67 sq ft more, 171 sq ft in all. The eaves take 104 pieces cut 11½″ from 9 panels, the rakes 68 from 6; with 10% extra, 10 vented and 7 solid panels (a carton of each), 17 fascia lengths for 176 ft of roof edge, 15 F-channel and 2 J-channel. The vented eaves give 1,491 sq in of net free area; the attic ventilation calculator asks 360 sq in low on the roof for this 1,500 sq ft attic at 1/300.

The same house with a hip roof (no gables): the eaves run all the way round, 164 ft with the four corners, so 164 sq ft of soffit: 16 vented panels (1 carton), 16 fascia lengths, 15 F-channel and 1 J-channel for the corners. Choosing the colors? The gutter and fascia color picker tries them on a house.

What siding costs, installed or the materials

Under Price it, the calculator prices the house with HomeGuide’s national ranges, read October 17, 2026. Installed prices the wall to side, 1,542 sq ft on the house in the quick answer; Materials only prices what you buy, the extra for waste included, 1,696 sq ft. HomeGuide prices fiber cement planks on their own: “Fiber cement siding planks cost $0.70 to $5.00 per square foot on average for the material alone.” For the others it gives the materials’ share of the job, and the calculator takes that share of the installed price. For vinyl: “The labor cost to install vinyl siding makes up around 50% of the total project cost, while materials make up the rest.” For engineered wood and wood: “Materials make up 50% to 55% of the total project cost, while labor makes up the remaining 45% to 50%.”

Soffit and fascia are priced by the foot of roof edge: “Soffit materials $2 – $5 (1’ wide) $4 – $10 (2’ wide); Total cost $4 – $11 (1’ wide) $8 – $22 (2’ wide), per linear foot.” and “Fascia board replacement costs $5 to $12 linear foot installed”. The calculator takes the 1 ft price for a soffit up to 12″ deep and the 2 ft price for a deeper one. The house above with 12″ eaves and rakes: 104 ft of eaves and 67 ft of rakes at $4 – $11 a foot and 176 ft of fascia at $5 – $12, about $1,600 – $4,000 installed, $1,000 – $1,900 for the materials. With a hip roof, $1,500 – $3,800.

Got a quote? Type the contractor’s total in Your quote. $9,000 for the vinyl house above is $5.84 a sq ft: inside the national range, in its middle. A quote below the range may leave out the old siding’s removal, the house wrap or the trim; one above it is worth a second quote, or a question about what it adds. These are national ranges in US dollars, and a local quote is the real price.

Worked examples

• 50 × 30 ft, one story, 2 gables at 6/12, 12 windows, 2 doors, a garage door, vinyl Double 4″: 1,600 sq ft of wall + 225 of gables − 283 of openings = 1,542 sq ft. With 10% extra, 1,696 sq ft: 9 boxes (18 squares), 15 starter strips, 23 J-channel, 11 finish trim, 4 corner posts and about 17 lb of roofing nails. About $6,200 – $10,800 installed.
• The same house, windows and doors left in: only the garage door comes off, so 1,762 sq ft, 1,938 with the extra: 10 boxes.
• The same house on two stories, HardiePlank 8¼″: 160 ft × 19 ft = 3,040 sq ft of wall, 2,982 to side. With 10% extra, 469 planks; James Hardie’s chart gives 426 for 29.8 squares before waste. 52 HardieTrim boards: 16 for the corners, 21 round the windows and doors, 9 for the frieze and 6 for the rakes. About $14,000 – $41,700 installed.
• 40 × 28 ft, one story, a 4/12 roof, 10 windows, 2 doors, a double garage door (2), vinyl Double 5″: 1,175 sq ft, 1,292 with the extra: 7 boxes, 12 starter strips, 22 J-channel.

Common mistakes

• Using the house’s floor area. A 1,500 sq ft home’s siding depends on its walls, not its floors: a one-story ranch has far more wall per square foot of floor than a two-story box of the same size. Measure the outside walls.
• Counting a plank’s full width. An 8¼″ HardiePlank shows 7 inches. Counting 8¼″ comes up 15% short.
• Forgetting the gables. Two gables under a steep 12/12 roof on a 30 ft end add 450 sq ft — four and a half squares.
• No waste. Every cut round a window and every angled cut in a gable leaves an offcut. Add 10%, more for a house with many gables or small windows.
• Buying J-channel by the window count alone. The gables’ rakes need it too, and they are long: about 17 ft a side on a 30 ft gable at 6/12.

Read next

• Modern rustic home exteriors
• Exterior color palette ideas
• Green house exteriors
• Lake house exteriors
• Make a mobile home look like a house

Choosing the color first? The free exterior house color visualizer paints it on a photo of your house. Painting instead of re-siding, the paint calculator counts the gallons for the same walls, and the 2D planner draws the house’s rooms to scale. Stucco instead of siding? The stucco calculator counts the bags of every coat for the same house.

Sources, read October 16, 2026: Georgia-Pacific’s Vinyl Siding & Accessories Version 21 Guide (panel and accessory lengths, pieces per carton); James Hardie’s HardiePlank Lap Siding Best Practices (the 12 ft plank, the coverage chart, the starter strip) and HardieTrim boards description; the Vinyl Siding Institute’s Vinyl Siding Installation Manual (2022); Kaycan’s vinyl siding calculator. Makers change their lines and cartons: your dealer’s label has the last word, and this page is re-checked every year. Prices, read October 17, 2026: HomeGuide’s house siding cost, vinyl siding cost, fiber cement siding cost and soffit and fascia replacement cost, national ranges re-checked every 6 months.