Free online siding 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.