Build a Deck Estimator

Complete decking material list — joists, deck boards, posts, fixings and concrete — from the deck dimensions.

Part of:Project Estimators hub
ft
ft
mm
mm

How to Use This Calculator

How to Use

  1. Choose metric or imperial units.
  2. Enter the deck length and width — boards are assumed to run along the length.
  3. Set the deck board width (144 mm is a common timber board) and joist spacing (400 mm is standard).

What this estimates

You get joist quantity and total length, the linear metres of decking boards, the number of support posts on a 1.5 m grid, the concrete for setting those posts, and an approximate screw count. Add joist hangers, a ledger board and post anchors to suit your design.

Common Questions

How far apart should deck joists be?

For most timber decking, joists at 400 mm centres are standard. Reduce to 300 mm if you lay boards diagonally or use thinner boards.

How many screws do I need for decking?

Plan for two screws at every point a board crosses a joist. Our estimate uses that rule — buy a little extra to be safe.

How deep should deck post holes be?

As a guide, set posts in holes about 600 mm deep with roughly 0.03 m³ of concrete each, deeper for tall or raised decks.

How far apart should deck joists be?

400 mm (16 in) centres is standard for most decking; 600 mm (24 in) can be used for thicker boards. Closer spacing gives a firmer, less bouncy deck.

Do I need to add waste for deck boards?

Yes, allow about 10% for cuts and the occasional damaged board — more for diagonal or herringbone patterns.

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