Decking calculator
Type in your deck size. See the boards, joists, screws and cost.
Standard widths: hardwood 63, 86 or 135 mm. Treated pine 70 or 90 mm.
At least 3 mm for hardwood up to 90 mm wide. 5 mm for treated pine.
Decking boards you need
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How does this decking calculator work?
It does the same sums a carpenter does when pricing a deck. Boards run along the length, and joists run across under them.
- Boards: the width of the deck, divided by one board plus one gap, gives the rows of boards. Rows times the length gives the metres of board. It adds 10% for offcuts, the allowance in Bunnings' merbau decking guide.
- Joists: one at each end, and none further apart than the spacing you pick.
- Screws: Timber Queensland says to fix each board at every joist with two nails, or with the maker's own fixings. So it counts 2 per board at each joist.
- Cost: the deck area times the built price per m² for your material, from What's The Damage's Gold Coast guide.
How many decking boards do I need?
Take a deck 6 m long and 4 m wide, with 86 mm hardwood boards and a 4 mm gap. Each board and gap takes 90 mm, so the 4 m width needs 45 rows. 45 rows of 6 m is 270 m of board. Bunnings' merbau decking guide says it is standard to buy 10% more than the deck needs, so order about 297 m.
Timber Queensland's deck sheet lists the standard board widths: hardwood 63, 86 or 135 mm, treated pine 70 or 90 mm, and cypress 68 mm. It says narrow boards shed water better, so they are less likely to cup and twist. Stagger the end joins, so boards side by side never join in the same place.
What joist spacing do decking boards need?
Timber Queensland's deck sheet fixes joists no more than 450 mm apart. Its decking table shows how far each board can span between joists:
| Board | Thickness | Max joist spacing |
|---|---|---|
| Hardwood | 19 mm | 500 mm |
| Hardwood | 25 mm | 650 mm |
| Cypress | 21 mm | 450 mm |
| Treated pine (H3) | 22 mm | 450 mm |
Timber Queensland, Residential Timber Decks data sheet (revised March 2014), checked 27 October 2026.
Composite boards are not in that table, so use the spacing in the maker's guide. Our deck joist spacing chart covers composite brands, diagonal boards and joist spans.
What does a deck cost to build?
Built prices on the Gold Coast run from $175 per m² for treated pine to $685 per m² for composite, according to What's The Damage. A high-set deck that joins a raised floor costs $49 to $175 more per m².
| Material | Per m² | A 25 m² deck |
|---|---|---|
| Treated pine | $175 to $345 | $4,375 to $8,625 |
| Merbau hardwood | $295 to $540 | $7,375 to $13,500 |
| Spotted gum hardwood | $345 to $590 | $8,625 to $14,750 |
| Composite | $275 to $685 | $6,875 to $17,125 |
A guide from published 2026 Gold Coast cost guides, not a quote. Brett's quote is the real number.
Our deck cost guide breaks the price down further.
How do I use the deck cost calculator?
Type in the size, pick your material, and tick the box if the deck joins a high-set floor. The calculator times the deck area by What's The Damage's Gold Coast price per m² for that material, built and finished. It is a guide, not a quote.
How many screws do I need for decking?
Two per board at every joist. For the 6 m by 4 m deck above, that is 45 rows times 15 joists times 2, or 1,350 screws. That is about 56 per m². Wider boards need fewer, because there are fewer rows.
What gap should I leave between decking boards?
Timber Queensland says at least 3 mm for hardwood and cypress boards up to 90 mm wide, and 5 mm for treated pine. Composite boards use the gap in the maker's guide. Our decking board spacing guide has the full table.
Does my deck need a balustrade?
Yes, if it is more than 1 m above the ground. Timber Queensland's deck sheet says those decks need a handrail or balustrade. The balustrade calculator works out the height and the gaps.
Planning a deck?
- Decks and patios on the Gold CoastNew timber and composite decks, pool decks and patios, plus repairs to the deck you have.
- Deck Cost per m2 on the Gold Coast (2026 Prices)Prices per square metre for pine, hardwood and composite decks.
- Deck Joist Spacing Chart for Australian DecksMost decks have joists at 450 mm. A chart by board type.
- Decking Board Spacing: How Big a Gap?Most decking needs a 3 to 5 mm gap. Side, end and wall gaps.
- Deck Footings: Types, Depth and Cost in AustraliaThe main types of deck footings, how deep they go and the costs.
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