Siding Calculator
Find how much siding you need for the walls of a house, a garage, or a shed. Enter the walls and gables, subtract doors and windows, and choose your vinyl or fiber cement siding to see the pieces, boxes, and squares to buy.
Add more walls or a triangle for each gable, and subtract doors and windows.
- Choose US or Metric. You can still change the unit of any single field.
- Enter the walls. For a single wall, choose Rectangle and enter its Length and Height. For all four walls of a rectangular house, choose Room walls and enter the outside length and width of the house and the wall height up to the eaves.
- For each gable, use Add section and choose Triangle. Enter the width of the wall below it as the Base and the height from the top of the wall to the peak as the Height.
- To leave out doors and windows, add a section for each one and set it to Subtract. Use Quantity for several of the same size.
- Choose the Siding profile. For another product, choose Custom size and enter the piece length and exposure from the label, and the pieces per box if it comes in boxes.
- Check the Waste allowance. It starts at 10%.
- Optionally, enter a price per piece, per box, per ft², per square, or per m² to estimate the cost.
Dimension fields accept whole numbers, decimals, fractions, and mixed
numbers, such as 40, 7.5, 3/4, or
12 1/2.
How much siding you need
The calculator finds the area of the walls and gables, subtracts the openings, adds the waste allowance, and divides by the area that one piece covers on the wall:
Total area = net wall area × (1 + waste % ÷ 100)
Pieces = total area ÷ (piece length × exposure), rounded up
Boxes = pieces ÷ pieces per box, rounded up
The exposure is the height of siding that shows on the wall. Each piece overlaps the one below, so the exposure is less than the full width of the piece, and using it counts the overlap. The calculator also shows the total area in squares. A square is 100 ft², the unit that siding and roofing makers use for area and for the size of a box.
With several sections, the calculator adds the sections set to Add and subtracts those set to Subtract. The area of each shape is calculated as follows:
| Shape | Area |
|---|---|
| Rectangle | length × height |
| Room walls | 2 × (length + width) × height |
| Triangle (base and height) | base × height ÷ 2 |
| Known area | the area you enter |
For Room walls, enter the outside length and width of the house and the height of the walls without the gables. That gives the four walls in one section.
A gable is the triangle of wall under the end of a roof. Its base is the width of the wall below, and its height is measured at the center, from the top of the wall to the peak. If you know the roof pitch instead, the height is base ÷ 2 × pitch ÷ 12. For a wall 30 ft wide with a 6/12 pitch, that's 15 × 6 ÷ 12 = 7.5 ft. To find the pitch from a rise and run, use the Roof Pitch Calculator.
The calculator subtracts doors and windows by their area, as James Hardie's coverage chart and Cedral's cladding calculator do. CertainTeed's vinyl siding estimating guide measures each wall including its doors and windows instead. If you don't subtract the small windows, the extra covers the cuts around them.
The calculator counts by area and doesn't lay out each course. The cuts at the ends of each course and around openings are covered by the waste allowance.
Siding profiles
The calculator lists common profiles for each region. The count depends only on the length and exposure of each piece, shown as the size below. Double 4 in vinyl comes 24 panels to a box and double 5 in vinyl 20, both 2 squares. The other profiles are sold by the piece.
| Profile | Size | Covers |
|---|---|---|
| Double 4 in vinyl | 12 ft 6 in × 8 in | 8.33 ft² |
| Double 5 in vinyl | 12 ft × 10 in | 10 ft² |
| 8 1/4 in fiber cement lap | 12 ft × 7 in | 7 ft² |
| 7 1/4 in fiber cement lap | 12 ft × 6 in | 6 ft² |
| 6 1/4 in fiber cement lap | 12 ft × 5 in | 5 ft² |
| 150 mm uPVC shiplap (UK) | 5 m × 150 mm | 0.75 m² |
| 190 mm fibre cement lap (UK and Europe) | 3.6 m × 160 mm | 0.576 m² |
| 180 mm fibre cement weatherboard (Australia and New Zealand) | 4.2 m × 150 mm | 0.63 m² |
The vinyl sizes are from Alside's Siding, Trim and Accessory Catalog (April 2026) for Odyssey Plus and Owens Corning's Select vinyl siding, which use the same lengths and exposures. Dutch lap panels of the same size count the same. The fiber cement sizes are from James Hardie's HardiePlank lap siding installation instructions and product data sheet. The metric sizes are from FloPlast's BBA certificate for its shiplap cladding, Cedral's UK fixing guide, and James Hardie Australia's Linea Weatherboard product page. These are guides. Check the label of the product you buy, and if it differs, choose Custom size.
Vinyl with the same exposure can come in other lengths and box counts. Alside's Charter Oak double 4 1/2 in panels, for example, are 12 ft 1 in long with 22 to a box. Enter such a product as a Custom size with its length, exposure, and pieces per box.
For fiber cement, the exposure is the width of the plank less the overlap. James Hardie's HardiePlank installation instructions call for an overlap of at least 1 1/4 in, and its coverage chart gives these exposures:
| Plank width | Exposure |
|---|---|
| 5 1/4 in | 4 in |
| 6 1/4 in | 5 in |
| 7 1/4 in | 6 in |
| 7 1/2 in (older charts) | 6 1/4 in |
| 8 in | 6 3/4 in |
| 8 1/4 in | 7 in |
| 9 1/4 in | 8 in |
| 9 1/2 in (older charts) | 8 1/4 in |
| 12 in | 10 3/4 in |
The 7 1/2 in and 9 1/2 in widths appear only in older versions of the chart. Each exposure is for the minimum overlap. For a width without a profile in the calculator, or if you overlap the planks more, choose Custom size and enter the actual exposure. James Hardie's chart rounds each count to the nearest plank, while the calculator rounds up, so it can be one plank higher: for 1 square of 8 1/4 in planks, the chart gives 14 and the calculator 15.
Cedral's planks overlap 30 mm, or 40 mm where walls take high winds. With a 40 mm overlap, choose Custom size and enter a 150 mm exposure. For James Hardie's 150 mm Linea Weatherboard, which has a 120 mm effective width, timber weatherboards, or other PVC cladding, choose Custom size.
Extra siding for waste
The waste allowance starts at 10%. CertainTeed's estimating guide suggests adding 10 percent for siding, soffit, and accessories, and Cedral's cladding calculator adds 10% to its plank count. James Hardie's coverage chart allows nothing for waste.
The allowance covers the cuts at the ends of walls, around doors and windows, and along the slope of each gable. CertainTeed adds 1 ft to the height of each gable for these cuts and notes that lower pitch roofs produce more waste. For a house with gables, dormers, or many corners, raise the allowance.
Trim, soffit, and accessories
The calculator counts the siding for the walls. Trim and accessories are sold by length, so measure them separately and divide by the length of the product to count the pieces:
- Starter strip: the length along the bottom of the walls.
- J-channel: the distance around each door and window, and along the eaves and gables where the siding meets the roof.
- Corner posts: the number of corners × the wall height.
Soffit covers the underside of the eaves. Its area is the width of the eave × its length, and soffit panels come in their own sizes.
Examples
A one-story house
A house 40 ft × 30 ft with 9 ft walls has 2 × (40 + 30) × 9 = 1,260 ft² of wall. Two gables 30 ft wide and 7.5 ft high add 30 × 7.5 ÷ 2 × 2 = 225 ft². Subtract ten windows 3 × 4 ft (120 ft²) and two doors 3 × 7 ft (42 ft²), and the net area is 1,323 ft², or 1,455.3 ft² (14.55 squares) with 10% added. A double 4 in vinyl panel covers 12.5 ft × 8 in, or 8 1/3 ft², so 1,455.3 ÷ 8 1/3 = 174.6, and you need 175 panels, or 8 boxes of 24.
Other profiles for the same house
With double 5 in vinyl at 10 ft² a panel, you need 146 panels, or 8 boxes of 20. With 8 1/4 in fiber cement at 7 ft² a plank, you need 208 planks. With 7 1/4 in planks you need 243, and with 6 1/4 in planks, 292.
Pricing per box or per square
If the vinyl is $90 a box, the 8 boxes cost $720.00. For an installed price of $350 per square, 1,455.3 ft² is 14.553 squares, so the cost is 14.553 × $350 = $5,093.55.
Metric dimensions
A wall 10 m long and 2.7 m high with a gable 8 m wide and 2 m high is 27 + 8 = 35 m², or 38.5 m² with 10% added. With 180 mm fibre cement weatherboards covering 0.63 m² each, you need 62 boards. With 150 mm uPVC shiplap at 0.75 m², you need 52, and with 190 mm fibre cement lap at 0.576 m², 67.
FAQ
It depends on the walls, not the floor area. Siding covers the length around the house times the wall height, plus the gables, less the doors and windows. A one-story house 40 × 30 ft with 9 ft walls and two gables 30 ft wide and 7.5 ft high, less ten 3 × 4 ft windows and two 3 × 7 ft doors, needs about 1,455 ft², or 14.55 squares, with 10% added. Enter your walls in the calculator to get your own number.
Your total wall area in ft² ÷ 100. For walls of 1,455.3 ft² with waste included, that's 14.55 squares. A box of double 4 in or double 5 in vinyl covers 2 squares.
12 double 4 in vinyl panels or 10 double 5 in panels, before waste. It's about 14.29 planks of 8 1/4 in fiber cement, 16.67 of 7 1/4 in, and 20 of 6 1/4 in. In metric, it's about 1.33 pieces per m² of 150 mm uPVC shiplap, 1.74 of 190 mm fibre cement lap, and 1.59 of 180 mm fibre cement weatherboard.
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