4 × 3 m deck: materials list and cost
A 4 × 3 m deck is 12 m². Built against the house, 450 mm off the ground, the materials come to about $3,192 in merbau or $4,294 in composite decking.
Merbau decking
$3,192
about $266 per m²
Composite decking
$4,294
about $358 per m²
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Materials list: merbau
| Item | Qty | Cost |
|---|---|---|
| Merbau decking boards 140 × 19 | 93 m | $925 |
| Merbau edge face board | 11 m | $109 |
| Joists 140 × 45 H3 treated pine, 4.8 m | 10 | $580 |
| Bearers 190 × 45 H3 treated pine, 4.8 m | 3 | $226 |
| Posts, with concrete and a stirrup (allowance of $100 each) | 12 | $1,200 |
| Joist hangers, screws and fixings (5%) | $152 | |
| Estimated materials total | $3,192 | |
Materials list: composite
| Item | Qty | Cost |
|---|---|---|
| Composite decking boards 137 × 23, 5.4 m | 18 | $1,768 |
| Composite edge face boards, 5.4 m | 2 | $196 |
| Hidden clip kits for composite (each covers 100 m of board) | 1 | $120 |
| Joists 140 × 45 H3 treated pine, 4.8 m | 10 | $580 |
| Bearers 190 × 45 H3 treated pine, 4.8 m | 3 | $226 |
| Posts, with concrete and a stirrup (allowance of $100 each) | 12 | $1,200 |
| Joist hangers, screws and fixings (5%) | $204 | |
| Estimated materials total | $4,294 | |
What this price assumes
- A plain rectangle, 4 m along the house and 3 m out from it.
- 450 mm from the ground to the top of the deck, with no stairs, balustrade or pergola.
- A treated pine frame: joists at 450 mm centres on bearers and posts, each joist cut from the shortest stock length that covers it.
- Bunnings “from” prices checked October 2026, plus 8% extra decking for offcuts. Prices vary by store and over time.
What changes the cost
- Height. A higher deck needs longer posts and more bracing. Decks more than 1 m off the ground need a balustrade.
- Stairs. Each set adds stringers and treads.
- Decking choice. Spotted gum, blackbutt and jarrah usually cost more than merbau. Treated pine decking costs less.
- Labour. These are materials only. Save your design and you can ask a local builder to quote the labour from it.
Other deck sizes
3 × 3 m4 × 3 m4 × 4 m5 × 3 m5 × 4 m5 × 5 m6 × 3 m6 × 4 m6 × 5 m6 × 6 m8 × 4 m8 × 5 mAll sizes
This is a guide only, not engineering or building advice. Spans, footings and post sizes depend on your site, height and local rules, so check your design with a builder or engineer before you buy or build.