Siding Calculator

The short version: add up the area of every wall, take out the windows and doors, then pad the total for waste. The catch is that a real house is never one clean rectangle — you've got gable ends, a garage that sticks out, maybe a bump-out for the kitchen. Miss one of those and you're back at the store mid-project. This calculator keeps each wall on its own line so nothing slips through, and it shows the math for every surface so you can double-check it against your tape measure.

Once it has your net wall area, it converts that figure into the units siding is actually sold in: squares (one square = 100 sq ft of coverage), then panels or boards, and finally boxes, so you can hand the numbers straight to a supplier or drop them into a cart.

Say you have a simple two-story box: front and back walls 30 ft wide × 18 ft tall, two side walls 24 ft × 18 ft, two gables (24 ft base × 8 ft rise), plus eight windows at 3 × 4 ft and two doors at 3 × 7 ft.

• Walls: (30×18×2) + (24×18×2) = 1,080 + 864 = 1,944 sq ft
• Gables: ½ × 24 × 8 × 2 = 192 sq ft
• Openings: (3×4×8) + (3×7×2) = 96 + 42 = 138 sq ft
• Net: 1,944 + 192 − 138 = 1,998 sq ft → with 10% waste ≈ 2,198 sq ft ≈ 22 squares

Plug those same numbers into the calculator above and you'll get the panel count, box count, accessories and a dollar range in one shot.

The formulas are the same ones professionals use on paper: sum the walls, add the gables, subtract the openings, pad for waste, convert to squares. That part is exact. The variables are coverage and price, which shift by product and market — we seed them from manufacturer guidance and typical US installed costs and show ranges so you're not misled by a single number. Always confirm the coverage on your actual product's box and get a local quote before ordering.

One figure rarely tells the whole story. Confirm these points and your siding estimate becomes an order you can actually place with confidence.

• Confirm coverage: the default coverage is a planning figure. Check the exact coverage printed on your product's box or spec sheet and adjust it if it differs, since even a small change moves the piece count on a big wall.
• Match the waste to your walls: keep 10% for a simple rectangular house, and raise it toward 15% for gables, dormers, bay windows and lots of angled cuts, because those details generate short offcuts you can't reuse.
• Account for accessories: starter strip, trim, inside and outside corners, flashing and fasteners are all part of a complete order, not an afterthought — the takeoff above estimates each so your material list is whole.
• Keep a spare: hold back a piece or a full box for future repairs, since profiles and colors get discontinued over time and an exact match years later is hard to find.
• Time your order: have material delivered close to the start date, stored flat and dry, so it isn't sitting exposed or getting damaged before the crew arrives.

Re-run the numbers above after any change and lean on the per-wall audit to verify each surface one at a time, so what you order matches what the wall actually needs rather than a rough guess. That small habit is the difference between one clean delivery and a mid-project trip back to the supplier.