Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate siding squares needed from your net wall area, the 100-sqft unit siding is conventionally ordered in.
Net area: 1350 sqft
15
Siding, like roofing, is conventionally ordered by the "square" -- 100 square feet -- borrowed from the same industry convention as roofing materials. This calculator nets out door and window openings from your total wall area first, then converts the result into whole squares to order.
Enter your total wall area, the combined area of doors and windows to subtract, and a waste factor (10% is a common default covering cuts at corners, trim, and breakage).
Net Area = Wall Area − Openings
Squares = (Net Area × (1 + Waste Factor)) ÷ 100, rounded up to a whole square
Once you know your squares, the Siding Cost Calculator turns that into a material and labor cost estimate using your own supplier's price per square.
Suppose a house has 2,000 square feet of wall area once you add every side, including the triangular gable ends, and 200 square feet of doors and windows. Net area is 1,800 square feet. With a 10 percent waste factor, that becomes 1,980 square feet, or 19.8 squares, so you would order 20 squares. If your siding has a lot of cuts, the waste percentage may need to rise.
Ten percent is a starting point, not a rule. Houses with many corners, dormers, bay windows, or a complicated roofline generate more offcuts. Diagonal or decorative installation patterns, and patterned shingle-style siding, also consume more material. Materials that must be matched carefully by batch or dye lot are worth over-ordering slightly, because a later purchase may not match in color.
The calculator gives siding panels or courses only. Trim, corner posts, J-channel, starter strips, house wrap, fasteners, and flashing are additional items that are typically bought by the piece or by linear foot, and they are not part of the number of squares. A supplier can help turn your measurements into a complete materials list.
As a sanity check, compare the squares figure with the exterior wall area you started with: it should be just over one hundredth of the net area, plus waste. If you got a very different result, look for a units mix-up, such as entering square yards or a wall length instead of an area.
Before you buy, confirm how many square feet one box or carton actually covers, since some products are sold by the carton rather than by the full square. Buy all of the material at once when you can, because lots produced at different times can vary slightly in color and gloss. Store leftover pieces flat and dry in case you need repairs later, and keep a note of the product name and color code for future matching.
It's a long-standing exterior construction industry convention (also used for roofing) -- 1 square always equals 100 square feet, regardless of the specific siding material.
Yes -- siding is typically packaged and sold by the square (or in fixed-size cartons that total a square), so a partial square still requires buying the full unit.
You can, but subtracting only larger openings is a common way to leave a cushion of extra material.
No. It only converts wall area into squares. Soffit and fascia are typically measured separately in linear feet.
The area math is the same, but coverage per box and the waste percentage can differ by profile, so use your product's own coverage information.