Timber Calculator Australia — Lineal Metres from Area
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Lineal metres
Board count by standard length
All standard lengths — boards needed
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How to calculate lineal metres of timber for any area in Australia
To find how many lineal metres of board are needed to cover an area, divide the area by the board width in metres (not including the gap). Then multiply by (board width + gap) / board width to account for spacing — or simply: LM = area ÷ (board width in m). Add your wastage percentage for cuts. To convert LM to board count, divide total LM by your chosen board length and round up. Australian standard timber lengths are 1.8 m, 2.4 m, 3.0 m, 3.6 m, 4.2 m, 4.8 m and 6.0 m. Availability varies by species and supplier.
Timber calculator — FAQs
What is the difference between lineal metres and square metres for timber?
Lineal metres (LM) measures total length regardless of width — it's how Australian timber merchants sell boards. Square metres (m²) measures area. To convert m² to LM, divide the area by the board width in metres (e.g. a 90 mm wide board: 20 m² ÷ 0.090 m = 222 LM). To convert LM to m², multiply by the board width. This calculator handles the conversion automatically including gap and wastage.
What gap should I leave between decking boards in Australia?
A 5–6 mm gap is standard for hardwood decking (spotted gum, blackbutt, merbau) installed in seasoned condition — it allows for minor movement and drainage. For softwood decking (pine, treated pine) installed unseasoned, use a 3–4 mm gap as the timber will shrink as it dries. Gaps less than 3 mm trap debris and moisture; gaps over 8 mm become a trip hazard and may not meet NCC requirements. A 5 mm spacer (cut from a piece of hardboard or offcut) is the easiest way to maintain consistent spacing.
What are standard decking board widths in Australia?
Common Australian decking board widths: 70 mm (narrow, for small decks or feature strips), 90 mm (the most common standard residential width), 140 mm (wide boards, less common, can show more cupping). Face widths are the dressed dimension — the actual coverage width after seasoning. A 90 mm board at 5 mm gap covers 95 mm per board run; this calculator accounts for that automatically.
How much extra timber should I order for wastage?
10% is standard for a simple rectangular deck or fence with straight cuts. Increase to 15% for L-shaped or irregular areas, and 20% for 45° diagonal patterns (which require significantly more cuts). Always round up to the nearest board — you can't buy half a board at the timber yard. Having a few boards left over is far less costly than a second delivery.
What is the best decking timber in Australia?
Hardwoods dominate Australian residential decking: spotted gum and blackbutt are extremely durable (Class 1–2 above ground) and native to eastern Australia; merbau (imported) is popular for its consistent reddish-brown colour; jarrah is valued in WA. All require proper gapping and fastening. Treated pine (H3 or H4 treated) is the budget option and widely available, but requires regular oiling to prevent surface checking. Composite decking is growing in popularity for its low maintenance but costs more upfront.
How to use this calculator
- Enter the area to cover in m². For a deck, this is the total deck surface area. For fencing, it's the fence length × fence height. For cladding, it's the wall area less doors and windows.
- Enter the board width in mm — use the face width (the visible width) of the dressed/finished board. Common Australian sizes: 70, 90, 140 mm for decking; 75, 100, 125 mm for fence palings.
- Enter the gap between boards. Leave at 5 mm for standard decking (accounts for spacing in the finished area).
- Set the wastage percentage. 10% for straight runs; 15% for angled layouts or irregular shapes.
- Select the standard board length you plan to buy. The results show board counts for all four standard lengths so you can compare options.
- Click Calculate. Results show total lineal metres and board counts for 2.4, 3.6, 4.8, and 6.0 m lengths.
Worked example: A 5.4 m × 3.6 m = 19.44 m² deck, 90 mm boards, 5 mm gap, 10% wastage. LM net = 19.44 ÷ (0.090 + 0.005) = 204.6 LM. With 10% wastage: 225.1 LM. Using 4.8 m boards: ceil(225.1 ÷ 4.8) = 47 boards. Using 6.0 m boards: ceil(225.1 ÷ 6.0) = 38 boards (fewer to handle but less flexibility on cutting).
Understanding your results
The lineal metres figure is the key number to present to your timber merchant when ordering. Australian timber is sold by the lineal metre (LM), not by the piece. Quote the total LM and the board section (e.g. "225 LM of 90×19 mm merbau decking") and the merchant will work out how many lengths to provide.
The board count table shows how many full-length boards you need for each standard length. Choosing a board length that matches your deck or fence run minimises wastage from end cuts — for example, a 5.4 m deck run is perfectly covered by 6.0 m boards (only 0.6 m trimmed per board), whereas 4.8 m boards leave a 0.6 m short run that requires a join.
Common mistakes: Using the nominal board width (e.g. the "90 mm" label) when the actual face width after dressing is slightly smaller — always confirm the actual coverage width with your supplier; forgetting to include the gap in the pitch calculation (a 90 mm board at 5 mm gap covers 95 mm, not 90 mm); and ordering for area only to discover the run direction doesn't match board length, requiring joins in every course.
Buying and specifying timber in Australia
Australian timber is sold in several ways, and understanding the terminology avoids costly mistakes when ordering. The key concepts are: dressed vs. sawn, nominal vs. actual size, and how standard lengths work.
Sawn vs. dressed: Sawn (rough sawn) timber is cut from the log at the specified size but is rough-textured and may vary ±2–3 mm. DAR (Dressed All Round) timber is planed on all four faces and is the standard for visible applications — decking, cladding, fencing, and interior joinery. The DAR process removes 3–5 mm from each dressed face; a "90 mm" board is typically 88–90 mm actual face width depending on species and supplier. Always confirm the actual coverage width.
Standard Australian lengths: Timber is stocked in 300 mm increments from 1.8 m to 6.0 m: 1.8, 2.1, 2.4, 3.0, 3.6, 4.2, 4.8, 5.4, 6.0 m. Hardwood lengths (spotted gum, blackbutt, merbau, jarrah) are less predictable — available lengths vary by species, mill, and season. Always confirm with your supplier before ordering.
Specifying timber for decking: In Australia, decking timber is typically specified by its face dimensions and treatment class. Hardwood decking for exterior use must be Class 1 or 2 above-ground durability. Treated pine is H3 for above-ground exterior exposure or H4 for ground contact. Merbau (a popular imported hardwood) is Class 1 and widely stocked; it bleeds tannins initially and should be allowed to weather before oiling. Spotted gum and blackbutt are Class 1–2 native hardwoods that handle Australian sun and rain extremely well.
Ordering tips: Order timber a minimum of two weeks in advance for hardwood species — they may not be in stock at your local Bunnings or Mitre 10 and need to be sourced from a specialist timber merchant. For large orders (100+ LM), get a quote from both a specialist timber merchant and Bunnings/Mitre 10. Specialist merchants often have better prices for hardwood but less flexibility on delivery. Always inspect the timber before accepting delivery — reject boards with excessive knots, cupping, bowing, or checking that will affect appearance or performance.
Australian standards and references
- AS/NZS 2271:2004 — Plywood and Blockboard for Exterior Use: not directly related, but referenced for timber product standards.
- AS/NZS 1604.1:2021 — Specification for Preservative Treatment: defines treatment classes H1–H6 for Australian conditions. H3 = above-ground exterior; H4 = in-ground contact; H5 = severe in-ground and marine.
- AS 5604:2005 — Timber: Natural Durability Ratings: classifies Australian timber species by durability class (1–4) for above-ground and in-ground applications. Class 1 is most durable.
- Australian Timber Database (Forest & Wood Products Australia) — species guides for durability, workability, and availability of Australian native and plantation timbers.