Siding Calculator
How many squares of siding a house takes, with doors and windows subtracted and a waste allowance matched to lap, board and batten, or shake.
Squares needed
11.85sq
With waste
1185ft²
Net wall area
1077ft²
A square of siding is 100 sq ft of coverage, which is how it is sold. Gable ends and dormers are not in this figure, so work out their triangular area and add it in if your house has them.
How the siding calculator works
It starts with your home's wall area, perimeter times height, minus the openings nothing gets sided over. A waste percentage goes on top for cuts and overlaps, and the total converts into squares, which is how siding is sold.
Formula: perimeter = 2 × (length + width). Gross area = perimeter × wall height. Net area = gross − (doors × 21) − (windows × 15). Total with waste = net × (1 + waste% ÷ 100). Squares = total ÷ 100.
Installing James Hardie fiber cement planks instead of standard lap siding? Use the Hardie Siding Calculator instead. It counts individual planks by exposure width, not squares.
Frequently asked questions
100 square feet of finished wall coverage. A square is the unit siding is bought and sold in, and it holds regardless of panel or plank size, which is the point of it. Divide your total wall area by 100 and that is what you order.
10% for horizontal lap siding, about 12% for vertical or board and batten, and 15% for shake or shingle, which involves far more cutting. A house with a lot of corners, bays, or trim detail can push past 20%. Every corner is two cut ends, and the offcuts rarely fit anywhere else.
No. This covers the rectangular wall area only, perimeter times height. Gable ends and dormers are triangles, so work each one out as half the base times the height and add them in before you order. A pair of gables on a normal house is easily another square or two.
Because averages of 21 sq ft per door and 15 sq ft per window are close enough for ordering material, and measuring every opening on a house takes an afternoon. If your place has a patio slider or a picture window, the average runs low, so measure those two and adjust by hand.
Yes. Vinyl is sold and installed in squares like most lap siding, so the area, waste, and squares math is identical. Fiber cement planks are the exception: use the Hardie siding calculator for those, since they get counted by the plank off length and exposure, not by the square.
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