Siding Calculator
Order siding by the square, not by guesswork.
Siding Calculator
Pieces = ceil(Area × (1 + waste) / coverage per piece); 1 square = 100 sq ft
Calculated instantly
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What This Calculator Does
The Siding Calculator estimates how many siding pieces, squares, and boxes an exterior job needs. It accounts for coverage per piece and a waste allowance for cuts, corners, and mistakes.
How It Works
Exterior wall area is increased by the waste percentage, then divided by the coverage of one piece and rounded up. One square is 100 square feet of wall area. Dividing the piece count by the number of pieces in a box gives the number of boxes to buy.
Example
For 1,200 sq ft of wall with 8 sq ft coverage per piece, 20 pieces per box, and 10% waste, the order area is 1,320 sq ft. That needs 165 pieces, 13.2 squares, and 9 boxes.
Formula
Pieces = ceil(Area × (1 + waste/100) / coverage per piece)Squares = Order area / 100Boxes = ceil(Pieces / pieces per box)Reading the Results
Siding pieces
Individual lengths or panels needed after waste. Use this when buying loose pieces rather than sealed boxes.
Squares
Order area in 100 sq ft units, the unit many siding suppliers quote in.
Boxes
Sealed boxes to buy, rounded up so you are not short of a matching dye lot.
Sources and References
International Residential Code (IRC) — exterior wall covering
Weather-resistant enclosure and clearance requirements
The IRC sets performance and clearance rules; coverage per piece comes from the manufacturer.
References identify the method or data behind this calculator. Where a standard or tariff changes, the current edition applies, and the assumptions stated above take precedence over a remembered figure.
Frequently Asked Questions
How much siding do I need for a 1,200 sq ft wall?
With 10% waste and 8 sq ft coverage per piece, you need 165 pieces, or 13.2 squares. That is 9 boxes if each box holds 20 pieces.
What is a siding square?
One square is 100 square feet of wall area. Suppliers use it because coverage per piece varies by profile and exposure.
Should I subtract windows and doors?
Yes for large openings. Subtract the opening area from the wall area, but keep small openings in the total because the offcuts around them are rarely reusable.
How much waste should I allow for siding?
Ten percent suits a simple rectangular elevation. Add 15% for gables, many corners, or diagonal installations, where offcuts are larger.