How Much Siding Do I Need?
Quick answer: add the area of every exterior wall, subtract ~21 sq ft per door and 12–15 sq ft per window, add 10% waste, then divide by 100 for squares of siding. A 1,200 sq ft ranch with 8 ft walls orders about 17–19 squares.
- Measuring wall area
- Subtracting doors and windows
- Lap exposure and coverage
- Worked example: 1,200 sq ft ranch
- Common mistakes
- FAQ
Measuring wall area
Walk the house and measure every exterior wall: length × height, added together. For a simple rectangle that's perimeter × wall height. Gables add triangular areas (base × height ÷ 2 each). Vinyl, wood and fiber-cement siding is sold in squares — 1 square = 100 sq ft of wall coverage, so the final number of squares is just your wall area ÷ 100.
Subtracting doors and windows
Openings don't get siding. Subtract about 21 sq ft per exterior door (a 3×7 ft door) and 12–15 sq ft per window (standard 3×4 to 3×5 ft). If you're installing trim around the openings, you can subtract slightly less — the trim job soaks up cutoffs anyway. For a house with 2 doors and 12 windows, that's about 42 + 165 = 207 sq ft of openings.
Lap exposure and coverage
Lap siding is sold as 12 ft planks with a stated exposure — the visible width between laps. At a 4-inch exposure a plank covers 4 sq ft per 12 ft length; at 6-inch exposure it covers 6 sq ft. The exposure (not the plank width) is what matters for coverage. Vinyl typically exposes 4–8 inches; wood bevel siding commonly 4–6 inches. The calculator handles this automatically — just pick your exposure.
Worked example: a 1,200 sq ft ranch
- Footprint 30×40 ft, walls 8 ft high → perimeter 140 ft × 8 = 1,120 sq ft
- 2 gables (30 ft wide, 8 ft tall): 2 × (30 × 8 ÷ 2) = 240 sq ft
- Total wall = 1,360 sq ft; minus 2 doors (42) and 10 windows (140) = 1,178 sq ft
- Add 10% waste = 1,296 sq ft
- ÷ 100 = 13 squares (order 14)
Common mistakes
- Using floor area instead of wall area. A 2,000 sq ft house has far more than 2,000 sq ft of exterior wall. Measure the walls, not the floor plan.
- Forgetting gable triangles. Gables add 100–300 sq ft on most homes — missing them shortchanges the order by 1–3 squares.
- Ignoring lap exposure. Ordering by plank width instead of exposure over-buys by 20–50%. Use the exposure number.
- No waste on long walls. Long runs mean planks rarely end clean at a corner — 10% waste is the floor, not the ceiling. Gables and complicated rooflines push to 15%.
FAQ
Add the area of all exterior walls, subtract doors and windows (about 21 sq ft per door and 12–15 sq ft per window), and add 10% waste. A 1,200 sq ft ranch with 8 ft walls needs about 17–19 squares of siding.
One square of siding is 100 square feet. Measure each exterior wall (length × height), add them up, subtract openings, add 10% waste, then divide by 100. 1,800 sq ft of wall ÷ 100 = 18 squares.
About 24–28 squares for a typical 2,000 sq ft two-story house — exterior walls total roughly 2,400–2,800 sq ft depending on the footprint.
Subtract about 21 sq ft per exterior door (3 ft × 7 ft) and 12–15 sq ft per standard window. If you plan to trim around openings, subtract a little less.
Add 10% waste for laps, cuts, corners and mistakes. Gable ends and complicated rooflines push that toward 15%. On 18 squares, 10% means ordering 20 squares.