How does the decking calculator work?
Enter the deck length and width, the board size, the gap, a waste allowance and the joist centres. It returns rows, lineal metres, boards with waste, joists and an estimate of clips or screws, and it prints each step so you can check the arithmetic.
What is a worked example?
A 5 by 4 m deck with 137 mm boards, a 5 mm gap and boards running along the 5 m side:
- Rows = (4,000 + 5) divided by 142 = 28.2, so 29 rows.
- Lineal metres = 29 times 5 = 145.
- Boards with 10 percent waste = 145 times 1.1 divided by 5.4 = 29.5, so 30 boards of 5.4 m.
- Joists at 450 mm centres = 5,000 divided by 450 = 11.1, so 12, plus 1 = 13 joists, each 4 m long.
What gap and spacing should I use?
ModWood requires a 4 mm side gap, Ekodeck’s Quickfix clip sets 3 or 6 mm and Futurewood gives 2 to 3 mm. Temperature changes end gaps: NewTechWood says a 5.4 m board needs 8.6 mm at 10 degrees and 2.2 mm at 40. Joist centres follow your board maker: 450 mm for most, 400 mm for Coastal, closer for diagonal boards. For the numbers by maker, see installing composite decking.
What isn’t counted?
Bearers, posts, footings, stairs, balustrades and fascia. Bearer and joist sizes come from the AS 1684 tables, as in WoodSolutions’ Table 2 for timber boards; see bearers and joists. For costs, use the decking cost calculator.
Questions
Is there a deck building calculator?
This one counts boards, joists and fixings for the surface. It doesn't size bearers, posts or footings, which come from AS 1684 tables or the frame maker's span tables.
How do I calculate a deck?
Rows = width divided by board width plus gap. Lineal metres = rows times the run. Boards = lineal metres times one plus waste, divided by board length. Joists = run divided by centres, plus one.
Is there a decking estimator or planner?
The calculator is both: it estimates materials and prints each step. It doesn't draw the deck, and it doesn't check approvals; see our deck-building guide for those.
What joist spacing should I enter?
The maximum your board maker states. For ModWood, Ekodeck Classic, Futurewood and NewTechWood Avenue it is 450 mm for residential use, with closer spacing for diagonal boards or commercial use.