Siding Calculator — Squares, Cartons & Cost
Estimate wall and gable siding area, 100-square-foot squares, full cartons, waste allowance, starter length, and cost.
Siding quantity begins with wall rectangles and triangular gables, expressed in square feet and 100-square-foot siding squares. A cut allowance and the selected carton coverage determine the full-carton order.
1,448 sq ft measured area · 15.93 siding squares after 10% allowance · 136 linear ft building perimeter.
- Siding8 cartons
- Starter strip planning length136 linear ft
Vinyl Siding Institute guidance commonly keeps ordinary windows and doors in the measured area as a waste allowance. Deduct only genuinely large openings when appropriate.
Vertical layouts, gables, dormers, corners, transitions, panel lengths, color lots, starter, trim, J-channel, flashing, fasteners, and manufacturer details can change the order.
This is a material-area estimate, not a wall, water-resistive barrier, fastening, wind-load, or code design.
Step by step
- 1
Measure each wall to the eaves and each gable separately, or enter a verified gross siding area.
- 2
Deduct only very large openings when appropriate; ordinary windows and doors often remain in the estimate as useful cutting allowance.
- 3
Enter the exact carton coverage and verify panel orientation, lengths, trim, starter, flashing, fasteners, color lot, manufacturer instructions, and local requirements.
Check the estimate before you buy
Estimate exterior siding area, 100-square-foot siding squares, full cartons, waste, starter-strip length, and material cost from building dimensions or known area.
A 40 × 28 ft building with 9 ft walls and two 28 × 8 ft triangular gables has about 1,448 sq ft of gross siding area. With 10% allowance, plan for about 1,593 sq ft, or 15.93 siding squares and eight 200-sq-ft cartons.
How the calculation works
Wall area is perimeter × eave height. Each triangular gable is base × height ÷ 2. Large openings can be deducted before waste is applied and the order is divided by exact carton coverage.
Siding Calculator — Squares, Cartons & Cost FAQ
Should I buy exactly the calculated amount of siding?
Usually no. Cuts, spillage, breakage, uneven surfaces, batch matching, and package rounding can increase the order. Use the editable allowance and confirm the product label.
Why does the result round up?
Stores sell full bags, boxes, cans, rolls, panels, or pieces. The tool keeps the mathematical amount visible, then rounds the purchasing quantity up separately.
What is a square of siding?
One siding square is 100 square feet of wall coverage. Carton coverage varies, so a carton is not automatically one or two squares.
Should I subtract windows and doors?
VSI estimating guidance says ordinary windows and doors are not usually deducted because their area provides allowance for waste. Consider deducting very large openings such as garage or sliding doors.
Reference: Vinyl Siding Institute installation and estimating manual. Results are practical estimates; complete labels, package directions, product specifications, and qualified professional advice take priority.