Siding Calculator
Enter the size of the house, the gable ends and the doors and windows to see how many squares of siding to order — as vinyl boxes or lap boards — plus starter strip, J-channel, trim and corner posts.
Enter the length, width and wall height of the house.
On this page
How to use the siding calculator
- Measure the footprint and wall height. Length and width of the house, and the height of the walls from where the siding starts to the eaves.
- Count the gable ends — the triangles under a gable roof — and enter the roof pitch. A hip roof has none.
- Count the openings. The calculator subtracts typical sizes for doors, windows and garage doors.
- Pick the siding type to see squares and vinyl boxes, or the number of lap boards for your exposure and board length.
How siding is calculated
Siding is sold by the square: 100 square feet of wall. Work out the wall area, add the gable triangles, subtract the openings, then add waste for cuts and overlaps.
Worked example: a 40 × 30 ft house with 9 ft walls, two 6/12 gables, 2 doors, 12 windows and a garage door
- Walls: 2 × (40 + 30) × 9 = 1,260 sq ft. Gables: 30 × (15 × 6 ÷ 12) ÷ 2 = 112.5 sq ft each, 225 sq ft for both.
- Openings: 2 × 21 + 12 × 15 + 112 = 334 sq ft, so the net area is 1,151 sq ft.
- With 10% waste: 1,266 sq ft = 12.7 squares → order 13 squares of vinyl (about 7 boxes of 2 squares).
- In fiber cement lap boards with a 7-inch exposure, each 12 ft board covers 7 sq ft: 1,266 ÷ 7 = 181 boards.
Trim and accessories
The siding itself is only part of the order. The calculator also estimates the lineal feet of the main accessories, in the 12½ ft lengths vinyl trim usually comes in:
- Starter strip along the bottom of every wall, except across doors and garage doors.
- J-channel around windows (all four sides) and doors (top and sides), and along the sloped rakes of the gables.
- Finish or undersill trim under the eaves, where the top course is cut.
- Outside corner posts on the four corners, usually 10 ft long — taller walls need two per corner.
Inside corners, window head flashing, soffit and fascia aren't included. Count them separately if your house has them.
Vinyl vs lap siding: buying tips
- Vinyl is priced and packed by the square. Most cartons hold about 2 squares, but check the label: the coverage depends on the profile (for example double 4-inch or double 5-inch).
- Fiber cement and engineered wood lap is sold by the board. Coverage depends on the exposure — the part that shows once boards overlap — not the full board width. An 8¼-inch fiber cement plank is usually installed with a 7-inch exposure.
- Waste: 10% suits a simple rectangle; houses with many corners, dormers or bays need 15% or more.
- Buy it all at once. Colors and textures can vary between production runs.
Frequently asked questions
How many squares of siding do I need for a 2,000 sq ft house?
The floor area doesn't tell you directly — siding depends on the wall area. A two-story 2,000 sq ft house often has 2,000 to 3,000 sq ft of wall, or 20 to 30 squares before openings and waste. Measure the walls to be sure.
How many square feet are in a square of siding?
100 square feet.
How much does a box of vinyl siding cover?
Usually about 2 squares (200 sq ft), but it depends on the profile, so check the carton.
Should I subtract windows and doors?
Yes for large openings like garage doors and patio doors. Many installers don't subtract small windows, which leaves extra for waste — the calculator subtracts them and adds the waste percentage instead.
Sources
- Industry convention of selling siding by the square (100 sq ft); fiber cement plank exposure from manufacturer installation guides (for example 7 in for 8¼ in lap planks).
- Gable area from triangle geometry and the roof pitch; see roof pitch explained. How we calculate.