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Deck Calculator

Deck Calculator

What is Deck Calculator?

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A deck calculator estimates the decking boards, joists, posts, and fixings needed to build a timber or composite deck. It also estimates the total cost based on material choice.

Calkulon makes complex calculations simple — built for students and everyday problem-solvers.

How to Deck Calculator

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  1. 1Calculate deck area (length × width)
  2. 2Board count: area ÷ (board width − gap) × board length; add 10% for diagonal or waste
  3. 3Joist spacing: typically 400mm centres; number = deck length ÷ 0.4 + 1
  4. 4Posts: typically every 1.5–2m where frame meets ground

Worked Examples

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Example 1
Given:4m × 3m deck · 140mm×28mm boards at 5mm gap
Result:~20 boards at 4m length

3m ÷ 0.145 = 20.7 runs

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Did you know?

Composite decking (wood-plastic) costs 2–3× more upfront than treated softwood but has a lifespan of 25+ years vs 10–15 years for softwood, making it often cheaper long-term.

Formula-verified for precision
Reviewed October 2026
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