onlinecalculator.me

Free online siding calculator

Siding is sold by the square (100 sq ft) or by individual boards and panels. Enter your wall perimeter, height, and opening count to get a precise material estimate for any siding.

About this calculator

How to use

  1. Enter wall height and house perimeter.
  2. Enter doors and windows to deduct their area.
  3. Choose your siding type.
  4. For lap siding, set the exposure in inches.
  5. Read squares, units, and lineal footage with waste.

Formulas

grossArea   = perimeter × wallHeight
wallArea    = grossArea − doors × 21 − windows × 15

areaWithWaste = wallArea × (1 + waste/100)
squares       = areaWithWaste / 100

Lap siding:
  coveragePerFt = exposure (in) / 12   (sq ft per lineal ft)
  linealFt      = areaWithWaste / coveragePerFt
  boards        = ceil(linealFt / 12)  (12-ft boards)

Panel siding (4×8 = 32 sq ft each):
  panels = ceil(areaWithWaste / 32)

Shingle siding:
  squares = ceil(areaWithWaste / 100)

Worked example

8-ft walls, 160-ft perimeter (40 × 40 house), 4 doors, 8 windows, lap siding at 7-in exposure, 10% waste:

grossArea    = 160 × 8 = 1,280 ft²
deductions   = 4 × 21 + 8 × 15 = 84 + 120 = 204 ft²
wallArea     = 1,280 − 204 = 1,076 ft²

areaWithWaste = 1,076 × 1.10 = 1,184 ft²
squares       = 1,184 / 100 = 11.84

coveragePerFt = 7 / 12 ≈ 0.583 ft²/ft
linealFt      = 1,184 / 0.583 ≈ 2,031 lin ft
boards (12ft) = ceil(2,031 / 12) = 170 boards

Notes

  • Include all gable triangles when measuring the wall area — they need siding too.
  • Add 2–3 extra squares for future repairs where color matching may be an issue.
  • Starter strips and J-channels are ordered separately by linear foot; measure all bottom edges, windows, and door openings.

Frequently asked

How do I calculate how much siding I need?
Find the gross wall area (perimeter × height), subtract door and window openings (21 sq ft per door, 15 sq ft per window), then apply a waste factor. Divide by 100 to convert to squares, or convert to boards based on your product's coverage.
What is siding exposure?
Exposure is how many inches of each lap board are visible after installation. A 7-inch exposure means each 12-foot board covers 7 linear inches of wall height. Wider exposure means fewer boards but a lower weather seal.
How are siding squares different from roofing squares?
Both equal 100 square feet of surface. The calculation is the same — divide net wall area by 100. Siding suppliers often sell pre-measured bundles (squares) so you can order by the square without doing extra math.
What waste factor should I use for siding?
10% is standard for rectangular walls with few obstructions. Increase to 15% for houses with many corners, dormers, or gabled walls that require more angled cuts.
How many 4×8 siding panels do I need?
Each 4×8 panel covers 32 sq ft. Divide net wall area by 32 and round up. For example, 1,000 sq ft of net wall area at 10% waste = 1,100 sq ft ÷ 32 = 35 panels.
How do I share my siding calculation?
Click Share for the plain page URL, or Share with my numbers to embed your dimensions in the URL.