Siding Square Footage Calculator
Calculate exterior wall area for siding installation. Subtract doors and windows, then add 10% for overlap and trim waste.
Siding Calculator
Calculating siding for a typical house
Add up the perimeter of all exterior walls, multiply by the wall height, and you have gross siding area. For a 30×40 ft single-story home with 9 ft walls, that's a perimeter of 140 ft × 9 ft = 1,260 sq ft.
Subtract the area of every door, window, and opening. Then add gable end areas if your home has gables. Finally, multiply by 1.10 to account for trim, overlap, and offcuts.
Don't forget gables
Gable ends are easy to miss. Each gable is a triangle: (base × height) / 2. For a 30 ft wide house with a 6/12 pitch roof, each gable is about 113 sq ft.
Two gables (front and back) add ~225 sq ft to your siding total — that's a meaningful chunk you don't want to leave out.
Pro tips
Measure each wall
Don't average — measure each wall separately, especially on irregular footprints.
Include gables
Gable ends are triangles: (base × height) / 2. Don't forget them.
Order full boxes
Vinyl siding is sold in boxes (about 200 sq ft each). Round up to the nearest box.
Add for trim
J-channel, corner pieces, and starter strips are sold separately. Get a contractor estimate or order 10% extra.