Siding Estimate Calculator
Perimeter = all wall lengths added together.
Roofing & Siding
Siding Calculator
Quick answer: siding area = perimeter × wall height + gables (width × height ÷ 2) − openings, plus 10% waste; squares = area ÷ 100. A 160 ft perimeter with 9 ft walls, two 30 × 7.5 ft gables, and 150 ft² of openings needs 1,667 ft² (16.7 squares) — 209 double 4 in vinyl panels.
Estimate exterior siding for a house or garage: wall and gable area, openings, waste, squares, and the number of lap siding pieces for vinyl, fiber cement, or any exposure and length, plus rough trim lengths.
Wall and gable areas
How to calculate siding
Siding is sold by the square (100 ft²) but installed by the piece, so an estimate has two stages: find the wall area that needs covering, then divide it by what one piece actually covers once it is lapped. The exposure — the part of each course left showing — is what matters, not the full board width.
Area = P × H + Σ(W × H ÷ 2) − openings
Pieces = Area × (1 + waste) ÷ (exposure ÷ 12 × length)
- Add up the wall lengths to get the perimeter, and measure wall height from the bottom of the siding to the eave or soffit.
- Multiply perimeter × height for the rectangular wall area.
- Add gable triangles: base width × height from eave line to peak ÷ 2 for each one.
- Subtract openings — garage doors, entry doors, and windows (width × height of each).
- Add waste: about 10% for a simple house, 12–15% for many gables, dormers, or short wall runs.
- Convert: divide by 100 for squares, and by the coverage per piece for a piece count.
Worked example
A 40 × 28 ft ranch has 10 ft walls, two 28 ft wide gables 7 ft tall (6/12 pitch), 12 windows of 15 ft² each, and two 21 ft² doors. It gets 8.25 in fiber cement planks at 7 in exposure in 12 ft lengths, with 10% waste.
- Walls: (40 + 28 + 40 + 28) = 136 ft × 10 ft = 1,360 ft²
- Gables: 2 × 28 × 7 ÷ 2 = 196 ft²; openings 180 + 42 = 222 ft²
- Net: 1,360 + 196 − 222 = 1,334 ft²; with 10% waste = 1,467 ft² (14.7 squares)
- Planks: each covers 7 ÷ 12 × 12 = 7 ft², so 1,467.4 ÷ 7 = 209.6 → 210 planks
Lap siding coverage per piece
Coverage = exposure ÷ 12 × length. Pieces per square rounded up, before waste. Check your product's actual exposure and length.
| Siding | Exposure | Length | ft² per piece | Pieces per square |
|---|---|---|---|---|
| Vinyl, double 4 in | 8 in | 12 ft | 8.0 | 13 (12.5) |
| Vinyl, double 5 in | 10 in | 12 ft | 10.0 | 10 |
| Fiber cement, 8.25 in plank | 7 in | 12 ft | 7.0 | 15 (14.3) |
| Fiber cement, 6.25 in plank | 5 in | 12 ft | 5.0 | 20 |
| Lap board, 16 ft | 7 in | 16 ft | 9.3 | 11 (10.7) |
Siding estimating tips and common mistakes
- Use exposure, not board width. An 8.25 in fiber cement plank lapped 1.25 in shows only 7 in; using 8.25 in undercounts by about 15%.
- Measure gable height from the eave line. The triangle starts where the wall height measurement stopped. For a gable roof, height = half the gable width × pitch ÷ 12 (a 30 ft gable at 6/12 is 7.5 ft tall).
- Don't forget dormers, bump-outs, and skirt walls. Add each as its own rectangle or triangle. Areas under a porch roof or behind a deck ledger are easy to miss.
- Trim is a separate order. Vinyl needs J-channel around openings and under rakes, outside and inside corner posts, starter strip, and utility trim under windows; fiber cement uses corner and window trim boards instead. Count them from the actual window list when you can.
- Buy one lot. Color and texture vary between production runs, so order everything — plus a few spare pieces for repairs — at once.
- Follow the installation guide. Vinyl must hang loose on its nails to expand, and fiber cement has clearance rules at the roof line and grade. Water-resistive barrier and flashing requirements are set by your local code.
Siding calculator FAQ
How do I calculate how much siding I need?
Multiply the wall perimeter by the wall height, add each gable triangle (width × height ÷ 2), subtract windows and doors, and add about 10% waste. A 160 ft perimeter with 9 ft walls, two 30 × 7.5 ft gables, and 150 ft² of openings is 1,515 ft² net, or 1,667 ft² (16.7 squares) with waste.
How many square feet are in a square of siding?
One square of siding covers 100 square feet of wall. A house needing 1,667 square feet of siding with waste needs 16.7 squares, which most suppliers round up to 17 squares or to full cartons.
How many pieces of vinyl siding are in a square?
A 12 ft double 4 in vinyl panel has an 8 in exposure, so it covers 12 × 8 ÷ 12 = 8 square feet, or 12.5 panels per square. A double 5 in panel covers 10 square feet, so 10 panels per square. Check the actual panel length, since many are slightly longer than 12 ft.
How many fiber cement siding planks do I need?
Divide the siding area by the coverage of one plank: exposure in inches ÷ 12 × plank length. An 8.25 in plank laid at 7 in exposure and 12 ft long covers 7 square feet, so 100 square feet needs about 14.3 planks. 1,334 square feet plus 10% waste needs 210 planks.
Should I subtract windows and doors when estimating siding?
Subtract large openings such as garage doors, patio doors, and big windows, but many estimators skip small windows because the offcuts around them are rarely reusable. Keeping 10% waste after subtracting openings covers cutting around them on a simple house.
How we built this calculator: results use the standard volume, area, and coverage formulas shown on this page, with typical U.S. material densities, bag yields, and waste factors that you can override. Written and checked by the YardsCalculator editorial team. Last reviewed: October 2026.