Decking Calculator AU

Work out how many boards, joists, bearers, posts and bags of concrete a timber deck needs. Metric, built around Australian timber sizes.

Deck size

Length along the boards (m) Width across the boards (m)

Decking boards

Board width (mm) 86 (86 x 19) 90 (90 x 19) 140 (140 x 19) 184 (184 x 19) Gap between boards (mm) Stock length (m) 3.0 4.2 5.4 6.0

Waste allowance is 10%. Butt joints need a joist under them.

Framing

Joist spacing (mm) 400450600 Joist size 90 x 45120 x 45140 x 45190 x 45

Bearer spacing (m) 1.21.51.82.4 Bearer size 90 x 45 single2 x 90 x 4590 x 70140 x 45

Post spacing along bearer (m) 1.21.51.82.4 Post size 90 x 90100 x 100115 x 115125 x 125

Post height above ground (m)

Post footings

Hole diameter (mm) Hole depth (mm)

One hole per post. Premix concrete: about 0.010 m³ per 20 kg bag.

Results

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Item	Qty	Length / volume

Order list

Estimates only, from the sizes you enter. Member sizes and spans must be checked against the AS 1684.2 timber framing span tables for your timber grade, wind class and footing class, or with your engineer. Pre-grooved decking needs a wider gap.