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  3. Decking

Decking Calculator

Calculate decking boards, joists, noggins, posts, and fixings needed. Full materials list ready for the merchant.

How to use the Decking Calculator

  1. Enter the deck length and width.
  2. Select the board width and joist spacing.
  3. Choose whether the deck is raised (requiring posts and bracing) or ground-level.
  4. Review the full materials list — boards, joists, noggins, posts, fixings, and brackets.

Why use this tool

  • Produces a complete materials list ready to take to the timber merchant.
  • Calculates joist spacing and noggin requirements for a structurally sound deck.
  • Includes fixings count so you do not run short of screws halfway through the build.

A well-built deck needs proper structural support beneath the boards. Joists should be spaced at no more than 400mm centres for standard 28mm softwood decking boards, or 500mm for thicker composite boards. Noggins between joists prevent twisting and add lateral stability. This calculator works out all the structural elements along with the decking boards themselves. It includes a waste allowance for cuts and also counts the number of fixings needed. The result is a complete shopping list that avoids the multiple trips to the merchant that turn a weekend project into a week-long one.

Part of Builder Tools Calculators — construction tools for UK tradespeople.

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