Siding Calculator
Enter your wall lengths and heights, add the gables and subtract the doors and windows to get the siding to buy. You get squares and cartons for vinyl, or planks for fiber-cement lap. Waste is included and editable.
Quick answer: 140 ft of 9 ft walls plus two 30 × 8 ft gables, minus 160 ft² of openings, is 1,340 ft² net; with 10% waste that is 15 squares, or 8 cartons of 200 ft².
Siding area is the wall area plus the gable triangles minus the doors and windows. Add a waste percentage, then divide by 100 ft² to get squares. Cartons come from the coverage printed on the carton, and lap planks from the exposure times the length.
Example: 140 ft of walls 9 ft high is 1,260 ft². Two gables of 30 ft by 8 ft add 240 ft², and 2 doors and 8 windows take off 160 ft². The net 1,340 ft² becomes 1,474 ft² with 10% waste, which is 14.74 squares, so 15 squares or 8 cartons of 200 ft².
Method
How this calculator works
The area is geometry. Coverage per carton and plank exposure are product facts that the calculator can only start with, so the number on your carton or in the manufacturer's installation guide should replace them.
Wall, gable and opening area
Each wall is length times height. A plain box house is the same sum as perimeter times wall height. Each gable end is the triangle above the wall. Doors, windows and other openings come off the total, and the net area never goes below 0.
Wall area = Σ (Length × Height)Gable area = ½ × Width × Rise × Number of gablesNet area = Walls + Gables − OpeningsWaste and the siding square
Siding is sold by the square, which is 100 ft² of wall coverage. Waste starts at 10%, a common contractor rule of thumb, and is editable from 0 to 30%. Gables, many openings and complex walls call for more. Some estimators fold gable cutting waste into the area with a width × height × 0.75 factor. This calculator keeps the exact triangle and the waste percentage separate so they do not stack by accident.
Area with waste = Net area × (1 + Waste ÷ 100)Squares = Area with waste ÷ 100Vinyl squares and cartons
Squares come from the 100 ft² definition in a siding manufacturer's estimating guide. A full vinyl carton is often 200 ft², two squares, according to editorial and retailer sources. That is medium confidence: coverage per carton is product specific, so use the number on your carton.
Squares to buy = ceil(Area with waste ÷ 100)Cartons = ceil(Area with waste ÷ Coverage per box)Fiber-cement lap planks
A lap plank covers its exposure times its length, not its full face. An 8.25 in board with 7 in of exposure at 12 ft covers 12 × 7 ÷ 12 = 7 ft². That pairing comes from a retailer specification and is medium confidence. No other width and exposure pair was verified, so none is preset. Exposure is the visible height of one course, not the board width. Take it from the manufacturer's installation guide.
Coverage per plank (ft²) = Exposure (in) ÷ 12 × Length (ft)Planks = ceil(Area with waste ÷ Coverage per plank)What each field does
| Field | What to enter |
|---|---|
| Which siding | Vinyl gives squares and cartons. Fiber-cement lap gives planks from the plank exposure and length. Other siding gives pieces from the coverage of one piece. |
| Wall length and wall height | One row per wall. For a plain box house, enter the whole perimeter, 2 × (length + width), as the length, and the wall height once. Add a row when the height changes, for example a one-story wing next to a two-story block. Or choose Known area if you already have the wall area. |
| Gable ends, width and rise | Each gable is a triangle: ½ × width × rise. Enter how many gables, the width of the wall under the gable and the rise from the top of the wall to the ridge. Set the count to 0 if there are none. A gable with a blank width or rise counts as 0, and the calculator warns you. |
| Doors and windows | The count and the area of one. The starting values (2 doors of 20 ft² and 8 windows of 15 ft²) are placeholders for the example house, so measure yours. Use Other openings for garage doors, large glass or anything else you will not cover. |
| Waste allowance | Starts at 10% and goes from 0 to 30%. Raise it for walls with many gables, corners or openings. |
| Coverage per box (vinyl) | Starts at 200 ft², two squares. This is a common carton size, not a rule. Read your carton, and clear the field to hide the box count. |
| Plank exposure and length (fiber-cement) | Exposure is the visible height of one course after it is overlapped, not the board width. The starting values are 7 in and 12 ft, which match an 8.25 in board. Use your manufacturer's installation guide for yours. |
| Coverage per piece (other siding) | The area one piece covers on the wall. The starting 8 ft² is a placeholder, not a product value. Replace it with the number on the label. |
| US and metric views | The metric view takes meters for lengths, square meters for areas and centimeters for plank exposure. The siding square (100 ft², about 9.29 m²) is still reported. |
Other siding: converting pieces per square to coverage per piece
Sold by the piece? Divide 100 ft² by the pieces per square on the label to get the coverage per piece, and enter it under Other siding. This table is from one manufacturer's estimating guide for vinyl. Piece length varies by product, so do not use it in place of your own label.
| Profile | Pieces per square | Coverage per piece |
|---|---|---|
| Double 4 in | 12 | 8.33 ft² |
| Double 4½ in | 11 | 9.09 ft² |
| Double 5 in | 10 | 10 ft² |
| 7 in board and batten | 17 | 5.88 ft² |
Not counted
Trim, J-channel, outside and inside corners, starter strip, soffit and fascia, house wrap or sheathing, flashing and fasteners are not part of this estimate. Siding manufacturers publish per-square factors for these accessories, so ask your supplier or use the maker's estimating guide for them.
Worked example: a house with 140 ft of 9 ft walls and two gables
Arithmetic checkedWalls with a 140 ft perimeter and 9 ft height, two gable ends of 30 ft width and 8 ft rise, 2 doors of 20 ft² and 8 windows of 15 ft², and 10% waste. The vinyl square count is the calculator's own example result.
| Step | Math | Result |
|---|---|---|
| Wall area | 140 × 9 | 1,260 ft² |
| Two gables | 2 × (½ × 30 × 8) | 240 ft² |
| Gross area | 1,260 + 240 | 1,500 ft² |
| Openings | 2 × 20 + 8 × 15 | 160 ft² |
| Net area to cover | 1,500 − 160 | 1,340 ft² |
| Net squares | 1,340 ÷ 100 | 13.4 squares |
| Add 10% waste | 1,340 × 1.10 | 1,474 ft² |
| Squares to buy | 1,474 ÷ 100 = 14.74, rounded up | 15 squares |
| Vinyl cartons of 200 ft² | 1,474 ÷ 200 = 7.37, rounded up | 8 boxes |
| Or fiber-cement planks (7 in × 12 ft = 7 ft²) | 1,474 ÷ 7 = 210.57, rounded up | 211 planks |
| You would order | 15 squares, or 8 boxes, or 211 planks | |
Disclaimer
Results are planning estimates based on the dimensions and assumptions you enter. They are not engineering, structural or building-code advice. Product yields, densities and coverage vary by manufacturer, batch and site conditions. Check product labels, your supplier and your local building department before you order materials or start work. Read the full calculation disclaimer.
Accuracy
What affects your estimate
The area is close to exact once you measure well. Coverage and waste depend on the product and the walls.
Coverage per carton is product specific
The 200 ft² carton is common, not universal. The coverage changes with profile and piece length. Check the label before you divide.
Exposure is not board width
For lap siding the exposure is what shows after overlap. Using the board width makes each plank look larger than it is and undercounts planks. For example, 8.25 in of width against 7 in of exposure.
Waste follows the shape of the house
A simple rectangle wastes less than a house with several gables, dormers and bump-outs. The 10% start is a rule of thumb. Raise it for cut-heavy walls.
Openings are your call
The calculator subtracts every door and window. Some installers do not deduct one or two small openings to leave some margin. To do the same, lower the counts or raise the waste.
Nailing, clearance to grade, wind rating and the weather barrier follow the manufacturer's installation instructions and local code. Cutting fiber-cement can release silica dust, so follow the maker's safety rules. Nothing here is structural advice.
Common mistakes
Entering the home's floor area as the wall area
Siding covers walls, not floors. The wall area of a 2,000 ft² house is a different number. Use perimeter times wall height for each story, plus the gables.
Forgetting the gables
The triangle above the wall is easy to skip. On the example house it is 240 ft², about 16% of the 1,500 ft² gross area.
Assuming every carton covers 200 ft²
Coverage per carton changes with the product. If your carton says something different, enter it in Coverage per box.
Leaving out the trim and accessories
This calculator counts siding only. J-channel, corners, starter strip, soffit and fasteners are separate items on your list.
Questions people ask
How do I calculate how much siding I need?
Add up the wall areas (length × height), add the gable triangles (½ × width × rise), subtract the doors and windows and add about 10% for waste. Divide by 100 to get squares. For the example house that is 1,340 ft², 1,474 ft² with waste and 15 squares. The guide on how to calculate square feet covers the area basics.
How much siding do I need for a 2,000 sq ft house?
It depends on the shape, not the floor area. As an illustration, a one-story 50 ft × 40 ft house has a perimeter of 2 × (50 + 40) = 180 ft, so 180 × 9 ft = 1,620 ft² of wall before gables and openings. A two-story house with the same footprint has about twice the wall height. Measure your own walls and enter them row by row.
What is a square of siding?
One square is 100 ft² of wall coverage, which is 10 ft by 10 ft. Vinyl siding is sold by the square, and a full carton is often two squares.
How many boxes of vinyl siding do I need?
Divide the area with waste by the coverage per carton and round up. At 200 ft² per carton, 1,474 ÷ 200 = 7.37, so 8 boxes. Use the coverage on your carton, because it changes with the product.
How do I calculate James Hardie or fiber-cement lap siding?
Choose Fiber-cement lap, then enter the plank exposure and length from the manufacturer's installation guide. An 8.25 in board at 7 in of exposure and 12 ft long covers 7 ft², so the example house needs 1,474 ÷ 7 = 210.57, which is 211 planks. Check that the exposure suits your product and your wall.
Can I use it for board and batten siding?
Yes, with Other siding. Enter the coverage of one piece. One manufacturer's guide lists 17 pieces per square for 7 in vinyl board and batten, which is 100 ÷ 17 = 5.88 ft² per piece. Your product's label comes first.
How do I find the rise of a gable?
The rise is the height from the top of the wall to the ridge. If you know the roof pitch, it is half the gable width times the pitch divided by 12. A 30 ft gable at 6/12 has a rise of 15 × 6 ÷ 12 = 7.5 ft. The roof pitch calculator helps with the pitch.
Related calculators and guides
Sources
Where the numbers come from
- Ply Gem how to estimate siding and accessories: one square is 100 ft², pieces per square by vinyl profile, accessed October 16, 2026.
- Inch Calculator (secondary source) vinyl siding calculator: sold by the square, subtract openings, 10% extra (editorial), accessed October 16, 2026.
- Hunker (secondary source) a box of vinyl siding is two squares, or 200 ft² (editorial; medium confidence), accessed October 16, 2026.
- Retailer specification for HardiePlank HZ5, 8.25 in × 144 in: exposure 7 in (medium confidence; read the manufacturer's guide for yours), accessed October 16, 2026.