Siding calculator
Wall area, openings, exposure and board length: you get linear footage and boards to buy, plus house wrap.
Purchase quantity
120 board
Net measurement: 559.723 ft² · Waste 10 %
- Siding boards120 board
- Board linear length1563.878 ft
- House wrap (75 m² roll)1 roll
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How it's calculated (visible formula)
linear = (area − openings) ÷ exposure; boards = ceil(linear × (1 + waste) ÷ board length)
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Measure gross area of each wall (including gables).
- Subtract doors and windows.
- Divide net area by board exposure for linear footage.
- Add 10–15% and divide by board length.
- Add house wrap, furring and trim.
Worked example: 645 sq ft wall, 86 sq ft openings, 4¾ in exposure
- 559 sq ft ÷ 0.396 ft ≈ 1,412 ft
- +10% ≈ 1,553 ft
- ÷ 12 ft boards ≈ 130
→ About 130 boards of 12 ft and 1 roll of wrap.
Common mistakes
- Using the full board width instead of exposure.
- Skipping a rainscreen gap behind the siding.
- Forgetting corner trim and flashing.
Pro tips
- Leave a ⅜–¾ in rainscreen gap with vertical furring.
- Start with a level starter strip.
- Stagger butt joints so they don't line up on consecutive courses.
- Seal cut ends with primer or the maker's sealer.
From calculation to quote
Add labour, overhead and your margin, and generate the professional PDF.
FAQs
- What is siding exposure?
- The part of each board left visible after the overlap.
- How much waste for siding?
- 10% on simple walls; 15% with many openings or gables.
- How many squares of siding?
- One square = 100 sq ft of wall coverage.
- What siding is lowest maintenance?
- Fiber cement and vinyl need the least; wood needs refinishing.
- How do I calculate siding squares?
- Net wall area in sq ft ÷ 100.
- Horizontal or vertical siding?
- Horizontal lap is most common; vertical needs horizontal furring for drainage.
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.