Siding is sold by the square, which covers 100 sq ft. Walls are rectangles, gables are triangles, and the openings come off, then a waste allowance goes on for cuts around windows and at the ends of the walls.
How to use this calculator
- Add up the length of every wall you will side, all the way around the house.
- Enter the wall height from the foundation to the eaves.
- Count the gables and measure one: its width at the base and its height at the peak.
- Count the windows and doors. Their areas are under More options; change them if yours are much bigger.
- Pick the siding. Fiber cement lap siding is counted in planks of the width you choose.
Worked examples
A ranch house in vinyl
Total length of the walls: 160 ft · Wall height: 8 ft · Gables: 2 · Gable width: 30 ft · Gable height at the peak: 6 ft · Windows: 12 · Doors: 2
- Siding
- 14.0 squares
- Cartons
- 7
- Area with waste
- 1,397 sq ft
- Walls
- 1,280 sq ft
- Gables
- 210 sq ft
- Taken off for doors and windows
- 220 sq ft
A two-story house
Total length of the walls: 140 ft · Wall height: 18 ft · Gables: 2 · Gable width: 28 ft · Gable height at the peak: 8 ft · Windows: 16 · Doors: 2
- Siding
- 27.4 squares
- Cartons
- 14
- Area with waste
- 2,741 sq ft
- Walls
- 2,520 sq ft
- Gables
- 252 sq ft
- Taken off for doors and windows
- 280 sq ft
Fiber cement planks
Total length of the walls: 120 ft · Wall height: 9 ft · Gables: 2 · Gable width: 24 ft · Gable height at the peak: 6 ft · Windows: 8 · Doors: 2 · Siding: Fiber cement lap, 8 1/4 in plank
- Siding
- 12.0 squares
- Planks
- 168
- Area with waste
- 1,197 sq ft
- Walls
- 1,080 sq ft
- Gables
- 168 sq ft
- Taken off for doors and windows
- 160 sq ft
A garage with no gables
Total length of the walls: 88 ft · Wall height: 9 ft · Gables: 0 · Windows: 2 · Doors: 1 · Siding: Other: squares only
- Siding
- 8.2 squares
- Area with waste
- 816 sq ft
- Walls
- 792 sq ft
- Gables
- 0 sq ft
- Taken off for doors and windows
- 50 sq ft
How siding is measured
A square of siding covers 100 sq ft. Walls are their length times their height. A gable is half its base times its height, and one vinyl maker suggests measuring the height 1 ft taller to allow for the angled cuts.
The same maker suggests adding 10 percent for waste on a large project. Vinyl siding comes in cartons of 2 squares for common double-lap panels, and fiber cement planks come 12 ft long, so the count depends on the plank's width.
Fiber cement planks per square
- A narrow plank shows less of its face, so it takes more pieces: the maker lists 25 planks per square for its narrowest plank.
- The most common width takes 14 planks per square.
- Its widest plank in this list takes 13 planks per square.
What to buy separately
- Starter strip along the bottom of every wall.
- Outside and inside corner posts, as long as the wall is tall.
- J-channel or trim around every window and door, and along the gable edges.
- House wrap under the siding, and the nails or screws the maker specifies.
Common questions
How do I measure my house for siding?
Multiply the total length of the walls by their height, add each gable as half its base times its height, subtract the doors and windows, and add the waste allowance. Divide by 100 sq ft for squares.
How many squares of siding are in a box?
One vinyl maker packs 2 squares in a carton of its common double-lap panels. Check the carton of the siding you buy, since profiles differ.
How much extra siding should I buy?
A vinyl maker suggests about 10 percent extra on a large project. Houses with many windows, gables or corners use more.
Do I subtract windows and doors?
Yes, take them off, then add the waste allowance back. The cuts around each opening use some of the material you saved.