Calculate decking boards, linear metres, screws and an optional New Zealand cost estimate. Enter your deck dimensions, board width, gap, stock length, waste allowance and joist spacing to build a practical materials list.
Suitable for homeowners, renovators, builders, landscapers and trade professionals preparing an initial decking estimate.
Last reviewed by NZ Calculator: 5 July 2026 · Estimated completion time: under two minutes
Deck area:Area = deck length × deck width
Board runs:Runs = round up [(distance across the boards + gap) ÷ (board face width + gap)]
Linear metres:Linear metres = board runs × distance each board run travels
Stock boards:Estimated stock boards = cutting-layout estimate × (1 + waste allowance)
The exact stock-board count can change with board lengths, staggered joints, picture framing, breaker boards and reusable offcuts. Use the result to prepare a supplier list, then confirm it against the final layout.
Calculating your materials…
Linear-metres comparison before waste, after waste and as full stock boards.
| Deck area | 0.0 m² |
| Board direction | — |
| Board runs across deck | 0 |
| Raw decking length | 0.0 lm |
| Decking length including waste | 0.0 lm |
| Full stock length purchased | 0.0 lm |
| Joist lines crossed per run | 0 |
| Estimated screw boxes | 0 |
| Planning purchase list | — |
| Decking boards | $0.00 |
| Screws | $0.00 |
| Subframe materials | $0.00 |
| Labour | $0.00 |
| Other fixed costs | $0.00 |
| Subtotal excluding GST | $0.00 |
| GST component | $0.00 |
| Estimated total including GST | $0.00 |
| Estimated total per m² | $0.00 |
The calculator first works out how many board runs are needed across the deck using the finished face width plus the selected gap. It then multiplies the number of runs by the distance each run travels to estimate raw linear metres.
The stock-board estimate uses the selected stock length and a simplified cutting layout before applying your waste allowance. This is more useful than dividing area by board width alone, but it is still a planning estimate because picture frames, breaker boards, stair edges, joins and reusable offcuts can alter the final order.
For fixings, the tool estimates the number of joist lines crossed by each board run, applies the selected screws per crossing and adds a separate fixing allowance. Butt joints can require extra fixings and must be supported correctly.
Linear metres per square metre depend on the finished board width and the installed gap. The table below shows common planning examples before waste.
| Board face width | Gap | Effective cover | Approx. linear metres per m² |
|---|---|---|---|
| 90 mm | 4 mm | 94 mm | 10.64 lm |
| 90 mm | 6 mm | 96 mm | 10.42 lm |
| 140 mm | 6 mm | 146 mm | 6.85 lm |
| 140 mm | 8 mm | 148 mm | 6.76 lm |
The actual order can be higher because boards are sold in fixed lengths and the layout may require joins, trimming and waste.
A 5 m × 4 m deck with boards running along the 5 m length, 140 mm boards and a 6 mm gap requires 28 board runs.
Raw decking length is 140 linear metres. With 10% waste, plan for about 154 linear metres, then convert that amount into the available stock lengths.
Using 90 mm boards with a 4 mm gap requires about 43 board runs across the same 4 m width.
That produces about 215 raw linear metres before waste because narrower boards require more runs.
Enter the actual board price per linear metre, fixing-box price, subframe allowance, labour rate and fixed costs.
The tool separates the GST component and shows an estimated project total and cost per square metre.
A useful deck-cost estimate should separate the visible decking boards from the supporting structure and construction work. The calculator can include:
Supplier prices and labour quotations change by region, timber species, treatment, access, height, foundations, details and finish. Enter current project-specific prices rather than relying on a generic national average. For an inclusive or exclusive tax check, use the GST Calculator NZ.
Decking gaps allow drainage, ventilation and seasonal timber movement. Published hardwood guidance commonly uses a minimum starting gap of 4 mm for 90 mm kiln-dried boards and 6 mm for 140 mm kiln-dried boards, while product type, moisture content, site conditions and climate can change the correct installation gap.
For general planning, published New Zealand guidance gives maximum joist centres of 450 mm for 19 mm timber decking and up to 600 mm for 32 mm decking. Those figures do not automatically apply to every deck. A barrier, cantilever, proprietary product or specific structural design can require closer spacing.
Hardwood installation guidance also recommends two pre-drilled fixings per board at each joist, with joins centred over support. Composite systems can use proprietary clips or different support requirements, so the manufacturer's instructions take priority.
Sources: BRANZ, slatted decking; Mitre 10 hardwood installation guidance; PlaceMakers radiata pine installation guidance.
The 3-4-5 method uses a right triangle to check that two set-out lines meet at 90 degrees. Measure 3 metres along one line and 4 metres along the other. When the diagonal between those marks is exactly 5 metres, the corner is square.
The same relationship can be scaled, for example 6-8-10. Check both deck diagonals as well: a rectangular set-out is square when opposite sides match and the two diagonals are equal. This set-out check does not replace plans, boundary checks or structural design.
Building Performance states that a deck generally does not need building consent when it is not possible to fall more than 1.5 metres, even if the structure collapses. The work must still comply with the New Zealand Building Code, and local planning rules or resource-consent requirements can still apply.
A safety barrier is required where there is a fall of one metre or more. Decks with a possible fall of more than 1.5 metres generally require building consent. Confirm the proposed work with the local council before construction.
Official sources: Building Performance deck-consent exemption guidance and barrier-design guidance.
Calculate how many board runs fit across the deck using the finished board width plus the installed gap. Multiply the number of runs by the distance each run travels, then add a waste allowance and convert the result into the stock lengths available from the supplier.
With a 6 mm gap, a 140 mm board has an effective cover of 146 mm. That requires approximately 6.85 linear metres per square metre before waste. The final stock-board order can be higher because boards are sold in fixed lengths.
It depends on the deck dimensions, board direction, board face width, gap and stock length. A 5 m by 4 m deck with 140 mm boards, a 6 mm gap and boards running along the 5 m length requires 28 board runs and 140 raw linear metres before waste.
A common visible-fixing estimate uses two screws per board at each joist crossing. Multiply the board runs by the number of joist lines crossed and by the screws per crossing, then include extra fixings for joins, losses and replacements. Follow the board and fixing manufacturer's instructions.
Ten percent is a common early planning allowance for a simple rectangular layout, but complex shapes, diagonal boards, picture frames, short stock lengths and selective colour matching can require more. Confirm the allowance against the final cutting plan.
The correct gap depends on species, moisture content, board width, product system, climate and site conditions. Published hardwood guidance uses minimum starting gaps of 4 mm for 90 mm kiln-dried boards and 6 mm for 140 mm kiln-dried boards. Follow the actual product instructions.
Published New Zealand guidance gives maximum centres of 450 mm for 19 mm timber decking and up to 600 mm for 32 mm decking in general situations. A barrier, cantilever, proprietary board or project design can require closer spacing, so do not use the calculator as structural approval.
There is no single reliable national figure because the result depends on board material, subframe, foundations, height, access, barriers, stairs, labour and region. Enter current board, fixing, structure and labour prices in the cost mode to create a project-specific estimate.
Possibly for a small, simple, low-level project, but the answer depends on area, structure, material, site work, labour and whether barriers or consent are required. Use the cost mode with current local prices rather than relying on a fixed budget rule.
A deck generally does not need building consent when it is not possible to fall more than 1.5 metres, but it must still comply with the Building Code and local planning rules. A barrier is required where the possible fall is one metre or more. Check the project with the local council.
It is a method for setting out a right angle. Measure 3 metres on one line and 4 metres on the other. When the diagonal between those marks is 5 metres, the corner is square. The method can be scaled to 6-8-10 or another equivalent ratio.
No. It estimates visible decking quantities, fixings and optional costs. It does not size or approve piles, bearers, joists, bracing, connections, barriers, stairs or foundations.
This calculator provides a high-level materials and cost estimate only. Actual board quantities, cutting layouts, fixings, prices, structural requirements, consent requirements and construction details can differ. Confirm the final design and order with project plans, the product supplier, your local council and an appropriately qualified building professional.
