Deck boards are counted in rows and lengths, not by area. Each row runs the length of the deck, and each row may need more than one board end to end.
Rows
Each row takes one board face plus one gap. A 145 mm board with a 5 mm gap takes 150 mm. A deck 3.6 m wide needs 3.6 ÷ 0.15 = 24 rows.
Australian boards are often narrower. A 90 mm board with a 5 mm gap is 95 mm a row, which is 38 rows across the same 3.6 m.
Lengths per row
Each row is as long as the deck. A 4.8 m run on 3.6 m UK stock needs two boards per row, because one is not long enough. On 5.4 m Australian stock one board covers it.
24 rows of two lengths is 48 boards. With 10% for cutting, that is 52.8, so 53. In Australia, 38 rows of one length is 38 boards, and 42 with waste.
| Market | Board face | Stock | Rows | Boards |
|---|---|---|---|---|
| UK | 145 mm | 3.6 m | 24 | 53 |
| Australia | 90 mm | 5.4 m | 38 | 42 |
Joists
Joists run under the boards at a set spacing. At 400 mm centres, a 4.8 m deck has 13 joist lines. Check the spacing for your board thickness and timber; thinner boards and composite boards often need closer joists.
B&Q lists a 3.6 m × 145 mm deck board, and a Bunnings merbau guide uses 90 mm and 140 mm faces. The stock length you can buy decides how many joins there are.
What is left out
The count does not include bearers, posts, screws or fascia. For posts set in concrete, the Postcrete calculator gives the bags.
Figures are estimates for a shopping list. Check the pack or datasheet before you buy.