Square metres in, lineal metres out
Timber yards don't sell area. They sell lengths of a profile, priced per lineal metre or per cubic metre, and it's on you to work out how many of them cover the floor, deck or wall you measured.
The whole sum turns on one number: how much width each board actually covers. Get that wrong by a few millimetres and the error multiplies across every board on the job.
Cover width is not board width
Two boards of the same nominal size can cover different amounts of floor:
- Tongue and groove — the tongue disappears into the next board. An 85mm floorboard with a 5mm tongue covers 80mm. Use the cover width from the supplier's spec sheet.
- Decking laid with a gap — an 86mm board at 4mm covers 90mm. Put 86 in the width box and 4 in the gap box.
- Shiplap and weatherboard — the lap eats width the same way a tongue does. Cover is always less than the overall size.
- Butt-jointed lining or cladding — cover equals the width. Gap is zero.
On a 15 m² floor, entering 85 instead of 80 leaves you about 11 lineal metres short — two lengths, found on the last afternoon when the pack has already gone back on the truck.
A worked example
A 4.2m × 3.6m room, hardwood overlay flooring 130mm wide × 19mm thick, laid with a 3mm expansion gap between boards, bought in 5.4m lengths.
- Area: 4.2 × 3.6 = 15.12 m²
- Cover per board: 130 + 3 = 133mm = 0.133 m
- Bare lineal metres: 15.12 ÷ 0.133 = 113.7 m
- Plus 10% waste: 113.7 × 1.1 = 125.1 m
- Lengths: 125.1 ÷ 5.4 = 23.2, rounded up = 24 lengths (129.6 m on the docket)
- Volume, if it's priced per cube: 125.1 × 0.130 × 0.019 = 0.309 m³
Australian stock lengths
Structural and dressed timber here comes in 300mm steps. These are the ones most yards actually hold:
| Length | Where it earns its keep |
|---|---|
| 2.4 m | Studs, noggins, short rails, palings cut from longer stock |
| 3.0 m | Small rooms, short deck runs, blocking |
| 3.6 m | The most common all-rounder — fence rails, joists, bearers |
| 4.2 m | Standard bedroom and deck widths without a join |
| 4.8 m | Long joists and bearers, most decking packs |
| 5.4 m | Decking and flooring — fewest end joints per square metre |
| 6.0 m | Longest commonly stocked; not held in every profile or species |
Longer isn't automatically better. If your run is 3.8m, a 4.2m length wastes 400mm and a 5.4m length wastes 1.6m. Match the stock length to the run before you match it to the price.
How much waste to allow
- 5% — a straight rectangular run you can order cut to length, no angles.
- 10% — the normal default. Covers end trims, a couple of split ends and the board you cut short.
- 15–20% — mitred or herringbone layouts, decks with returns or angled edges, recycled or feature-grade stock where you're culling boards for defects.
Order the whole job in one hit if you can. A second pack from a different run of hardwood can come back a visibly different colour, and nobody looks at the invoice when they're looking at the floor.
Buying by the cubic metre
Rough-sawn and structural hardwood is often quoted per cubic metre, dressed timber per lineal metre. They're hard to compare in your head, which is exactly why one supplier looks cheap until the delivery lands.
The volume figure above lets you compare them properly: divide a per-cubic-metre price by the volume per lineal metre and you have the same number twice. For 130 × 19 board that's 0.00247 m³ per lineal metre, so $2,400 a cube works out at about $5.93 a lineal metre before delivery.
One catch — cubic metre pricing is usually quoted on the nominal size, not the dressed size. A board sold as 150 × 25 might measure 138 × 19 once it's been through the machine. Ask which size the price is against before you compare two quotes.
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Try Yamate free → Free to try · no card · sign in with a link, no password to rememberTimber & lineal metres FAQ
How do I convert square metres to lineal metres?
Divide the area in square metres by the cover width of one board in metres. A 20 m² floor with boards covering 90mm is 20 ÷ 0.09 = 222 lineal metres, before waste.
What is the difference between lineal metres and square metres?
A lineal metre is a metre of length of one board, whatever its width. A square metre is area. Timber is sold by the lineal metre, jobs are measured in square metres, and the board cover width is what connects them.
What lengths does timber come in Australia?
In 300mm steps, most commonly 2.4, 3.0, 3.6, 4.2, 4.8, 5.4 and 6.0 metres. Not every profile or species is stocked in every length — check before you plan a run around 6.0m.
How much waste should I allow on timber?
Ten per cent on a straight run is the usual allowance. Push it to fifteen or twenty if there are angles, a herringbone layout, or you're culling feature-grade boards for defects.
Do I count the gap between decking boards?
Yes — it is part of what each board covers. An 86mm board at a 4mm gap covers 90mm, so it takes about 4% fewer boards than the bare width suggests. Enter the width and the gap separately above.
How do I work out cubic metres of timber?
Lineal metres × width in metres × thickness in metres. 100 lineal metres of 130 × 19 board is 100 × 0.130 × 0.019 = 0.247 m³. Use it to compare a per-cube price against a per-lineal-metre one.
Other calculators you'll want
General information for Australian trades, and an estimate only — not tax, financial or legal advice. It is not engineering, building or design advice either: a calculator works out a quantity from the figures you enter, and anything that needs sign-off still needs your engineer, certifier or building surveyor. Board widths, cover widths and stock lengths vary by supplier, species and profile — confirm yours against the spec sheet before ordering. This is a materials estimate to help you order and quote, not a structural specification. Sizes and spans for anything load-bearing come from AS 1684 and your supplier's engineering data.