Siding Calculator

Estimating siding follows the same take-off a contractor uses: measure every wall, add the triangular gable ends, subtract the openings that need no siding, then add a waste allowance for cuts and corners. The result converts to siding squares, the industry's 100 sq ft ordering unit.

In one formula: total = ((wall length x wall height) + (0.5 x gable base x gable height) - opening area) x (1 + waste / 100). Every input above maps to one term.

Take a house with 160 ft of total wall length and 10 ft walls: 1,600 sq ft of wall. Two gable ends, each 30 ft wide and 8 ft tall, add 0.5 x 30 x 8 x 2 = 240 sq ft. Ten windows at 3x4 ft subtract 120 sq ft; two doors at 3x7 ft subtract 42 sq ft.

Gross is 1,840 sq ft, openings are 162 sq ft, net is 1,678 sq ft. With 10% waste: 1,678 x 1.10 = 1,845.8 sq ft, or 18.46 squares. Order 19 squares; the spare covers repairs.

A siding square is 100 square feet of wall coverage, and it is how siding is sold, priced, and estimated across the industry. Divide your total square footage by 100 and round up: 18.46 squares means ordering 19.

Contractors price installed siding per square too, roughly $300-$700 per square for vinyl and more for fiber cement, which is why the square is the natural unit for both material and cost estimates.

Ten percent is the standard waste allowance for a simple rectangular house: it covers cutting waste around openings, corner trim, and damaged pieces. Complex houses with many corners, gables, dormers, or diagonal cuts need 15-20%.

Measure wall length along the base of every wall you are re-siding and add the lengths together; a 30x50 ft house sided on all four walls is 160 ft. Measure height from the bottom edge of the siding to the soffit, and run the calculator once per section if heights differ.

For each gable, measure the base width and the height from the eave line to the peak; for two matching gables, enter twice the width in one go. Do not bother subtracting small vents or outlets: only openings over a few square feet move the total.

The square footage covers the siding itself. Trim is estimated separately: starter strip runs the full wall length plus 10%, and J-channel wraps each opening. Fasteners, house wrap, and flashing are separate line items a contractor's quote will break out.

For the roof that caps those gables, the roofing calculator runs the same area logic upward, and the paint calculator covers the same walls in gallons.