Siding Calculator
Use this siding calculator to estimate how many siding pieces, squares, trim pieces and rolls of housewrap you need to cover the outside of a house. Enter the building size, gables, windows and doors, and get a shopping list with waste already built in.
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How to Use This Siding Calculator
Start with your building's length, width and wall height in feet, then choose how many gable ends the house has and the rise of each one. Add the windows, doors and garage doors that interrupt the siding, pick a siding product (or type your own piece length and exposure), and set a waste allowance. Press Calculate to get the number of siding pieces and squares to order, plus a matching list of starter strip, J-channel, corner posts and housewrap rolls.
Why This Matters
Siding is one of the biggest exterior purchases most homeowners ever make, and the quantity you order drives both the budget and the schedule. A typical two-story house with a 1,000 sq ft footprint has roughly 1,800 to 2,500 sq ft of exterior wall, which is 18 to 25 squares, and every square of vinyl or fiber cement adds up quickly once labor is included. Order too little and the crew waits for a second delivery. Worse, siding is made in production runs, so a later order can differ slightly in color or sheen from the first. Order too much and you have money sitting in leftover bundles that most suppliers will not take back once opened.
Contractors, DIY remodelers, landlords comparing bids and insurance adjusters scoping storm repairs all need a quick, defensible number. A bid that quotes 14 squares for a house you measure at 11 deserves a question. A bid that quotes exactly the net wall area with no waste is a risk to you, because every cut, corner and mistake eats into the order. This siding calculator gives you a baseline to check quotes against and a shopping list you can take straight to the supply yard.
How It's Calculated
The calculator uses the standard area takeoff that estimators use, with every quantity rounded up rather than down:
Perimeter = 2 × (length + width)
Wall area = perimeter × wall height
Gable area = gable ends × ½ × width × rise
Gross area = wall area + gable area
Net area = gross area − (openings × deduction %)
Area to order = net area × (1 + waste %)
Coverage per piece = piece length × exposure ÷ 12
Pieces = area to order ÷ coverage per piece, rounded up
Squares = area to order ÷ 100, rounded up to 0.1
Accessories follow the same logic. Starter strip is the perimeter plus 10% divided by 12.5 ft lengths. J-channel covers the perimeter of every window, door and garage door plus the sloped rake edges of each gable (the slope length is √((width ÷ 2)² + rise²)), plus 10%, divided by 12.5 ft. Outside corners are four corners times the number of 10 ft posts needed for the wall height plus 6 in. Housewrap is the gross area plus 10% divided by 900 sq ft, the coverage of a 9 × 100 ft roll.
This tool follows common estimating rules of thumb, not a code calculation. The International Residential Code (R703) calls for a weather-resistant exterior wall envelope with a water-resistive barrier and flashing, and siding must be fastened and spaced according to the manufacturer's installation instructions. Local codes and wind-zone requirements vary. The result is a materials estimate, not engineering, permit or inspection approval.
Worked Example
Take a 40 ft × 24 ft house with 9 ft walls, two gable ends rising 6 ft, eight 3 × 5 ft windows, two 3 × 6.67 ft doors and one 16 × 7 ft garage door, covered in Double 4 vinyl with 10% waste. These are the calculator's default values.
- Perimeter = 2 × (40 + 24) = 128 ft. Wall area = 128 × 9 = 1,152 sq ft.
- Gable area = 2 × ½ × 24 × 6 = 144 sq ft. Gross area = 1,152 + 144 = 1,296 sq ft.
- Openings = 120 (windows) + 40.0 (doors) + 112 (garage) = 272.0 sq ft. Net area = 1,296 − 272.0 = 1,024.0 sq ft.
- With 10% waste: 1,024.0 × 1.10 = 1,126.4 sq ft to order.
- Each 12.5 ft piece with 8 in. exposure covers 12.5 × 8 ÷ 12 = 8.33 sq ft, so 1,126.4 ÷ 8.33 = 135.2, which rounds up to 136 pieces, or about 11.3 squares.
- Trim: 128 × 1.1 ÷ 12.5 rounds up to 12 starter strips. J-channel is about 266 ft, plus 10%, which makes 24 lengths. Corners need 4 posts. Housewrap is 1,296 × 1.1 ÷ 900, which rounds up to 2 rolls.
Tips & Common Mistakes
- Measure the wall, not the floor plan. Bump-outs, bay windows, dormers and porch returns add wall area. Run the calculator once per section and add the results.
- Check your product's real coverage. Exposure and length vary by brand and profile. Read the carton or spec sheet and use the Custom option if it differs from the presets.
- Use 15% waste for cut-up houses. Many gables, angles, short walls and diagonal cuts at rakes waste more than a plain box. Use 5–10% only for simple rectangular walls.
- Buy everything from the same lot. Order all siding at once and check the lot or run number on each carton so color stays consistent across the house.
- Do not skip the water-resistive barrier and flashing. Housewrap, window flashing and kick-out flashing at roof-to-wall joints keep water out. Follow the manufacturer's nailing, expansion-gap and clearance rules, and ask your local building department what applies.
Frequently Asked Questions
How much siding do I need for a 2,000 sq ft house?
It depends on the shape and height of the walls, not the floor area. A two-story house with a 1,000 sq ft footprint often has 1,800 to 2,500 sq ft of wall before openings. Enter your actual dimensions into the siding calculator for a closer number.
What is a square of siding?
A square is 100 square feet of wall coverage. Vinyl siding is usually sold by the square, while fiber cement and wood siding are usually sold by the piece or plank. This calculator gives you both.
How much waste should I add to a siding order?
Plan on 10% for a simple house and 15% when there are many gables, corners, dormers or diagonal cuts. Go to 20% if you are a first-time installer or the layout is complex. A short order is usually far more costly than extra bundles.
Do I subtract windows and doors from the siding area?
Yes, normally. Large openings such as garage doors and picture windows are deducted in full. If you want extra margin, choose the 50% deduction option, because the cut-around pieces around openings produce more scrap.
How many pieces of vinyl siding are in a square?
For Double 4 panels that are 12.5 ft long with 8 in. exposure, each piece covers about 8.33 sq ft, so a square is 12 pieces. Double 5 panels cover about 10.4 sq ft each, so a square is about 10 pieces.
Can I use this siding calculator for fiber cement, wood or board-and-batten?
Yes for lap-style products. Pick a fiber cement preset or choose Custom and enter the plank length and exposure. For board and batten, enter the effective coverage width of a board (the board width minus any overlap) as the exposure. Also add extra for the battens, which are a separate item.