How the siding calculator works
Siding is sold and priced by the square (100 square feet). The calculator adds the rectangular walls and the triangular gable ends, then subtracts doors and windows.
Walls = 2 × (length + width) × height
Gables (2) = width² × pitch ÷ 24 · Squares = net area × (1 + waste) ÷ 100
Example: a 40 × 30 ft house with 9 ft walls and a 6/12 gable roof
The walls are 2 × 70 × 9 = 1,260 square feet, and the two gables on the 30 ft ends add 225. Two doors and twelve windows take out 222, leaving 1,263 square feet. With 10% extra that's 13.89 squares, about $5,557 at $400 a square.
Trim, J-channel, corner posts, soffit and housewrap are extra. Most vinyl siding comes 2 squares to a box.
Frequently asked questions
How many squares of siding does a house need?
A typical 1,500 to 2,000 square foot two-story house needs roughly 20 to 30 squares, but measure your walls to be sure.
Should I subtract windows and doors?
Yes for large openings. Small windows are sometimes left in to cover waste; the calculator subtracts them and adds a separate waste allowance.
Last reviewed: 2026-10-31