Calculateus

Siding Calculator

Calculate how many squares of siding you need for your home's exterior walls.

Result

Siding Squares Needed
18.15
Net Wall Area
1,650 sq ft (153 m²)

One "square" of siding equals 100 square feet of coverage - a term borrowed from roofing that most siding manufacturers still use.

About the Siding Calculator

Siding is priced and ordered by the square, a 100 square foot unit borrowed from roofing, and subtracting doors and windows before applying a waste allowance keeps the estimate from running high.

How It Works

The calculator subtracts your door and window area from the total exterior wall area, adds your waste percentage to the remaining net area, then divides by 100 to convert to siding squares.

squares = (max(wall area - openings, 0) × (1 + waste %)) ÷ 100

Examples

A typical single-story home

1,800 sq ft of wall area minus 150 sq ft of doors and windows leaves 1,650 sq ft, which at 10% waste comes to about 18.15 squares.

A home with more openings

The same wall area with 250 sq ft of openings instead leaves only 1,550 sq ft net, coming to about 17.05 squares, notably less material.

Advantages

  • Subtracts openings before calculating, avoiding an inflated estimate
  • Shows results in both siding squares and net area with metric conversion
  • Applies a standard waste allowance for cuts and trim losses

Common Mistakes

  • Not measuring gable ends and dormers as part of the total wall area
  • Forgetting to subtract door and window area before calculating squares
  • Not budgeting separately for trim pieces like J-channel and starter strip

Edge Cases to Watch For

  • Gable ends and dormers add wall area beyond simple rectangular wall sections, and should be measured and added into the total separately.
  • Lap siding profiles vary in exposed width, which affects labor and appearance but not the underlying square footage calculation here.
  • Corner trim, J-channel around openings, and starter strip are separate trim materials not included in the siding square estimate.

Common Use Cases

  • Ordering siding for a full exterior re-side project
  • Budgeting a siding replacement after storm or rot damage
  • Comparing material needs across different waste allowances
Written & fact-checked by the Calculateus TeamLast updated August 5, 2026How we verify our formulas

Frequently asked questions

How do I measure total exterior wall area for an irregular house?

Measure each wall section (height × width) separately and add them together, including gable ends - it's more accurate than trying to estimate the whole perimeter at once, especially on homes with bump-outs or varying wall heights.

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Conclusion

Squares are just net area divided by 100, but measuring every wall section, including gables, is what keeps the total accurate. Budget separately for trim materials, since corner posts and J-channel are priced and ordered apart from the field siding itself.