How many decking boards do I need?
Work out the deck area, allow for the gap between boards and the cuts, and get the linear metres of board, the number of boards, and the joists underneath. A 5 mm gap between boards matters more than people think — it adds up over a wide deck. Free, no sign-up.
A guide, not a guarantee. The board count is the deck width divided by the board-plus-gap; the joist count is a rough across-the-width figure at your spacing — a real frame needs perimeter and noggin timbers too. Composite decking has its own fixing and spacing rules; follow the maker's instructions. Joist timber, fixings, a weed membrane and ground prep are all extra. Nothing you type leaves your browser.
Boards across, then the run, then the joists.
Count the boards across the width. Each board plus its gap covers a fixed strip — a 144 mm board with a 5 mm gap is 149 mm. We divide the deck width by that and round up, so the last board may need ripping down to fit.
Work out the run. Each row of boards runs the deck length. Boards by the row, times the rows, gives the total linear metres, and we add wastage for the cuts and any end-to-end joints over a joist. Lay boards in one length where you can — joints are weak points and trip hazards.
Then the boards to buy. Divide the linear metres by your board length and round up. A few spare lengths are worth having for a future board that warps or splits.
The frame underneath. Joists carry the boards and stop them flexing. 400 mm centres suit most timber decks; drop to 300 mm for composite boards, a diagonal lay or a deck that'll take heavy use. The joist figure here is a rough count across the width — a proper frame also needs the outer perimeter joists and noggins between them.
What this leaves out. Joist timber, decking screws or hidden clips, joist tape, a weed membrane and the ground prep or sub-frame supports are all separate. Set a slight fall across the deck so water runs off.
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Stead remembers your garden and outdoor jobs, what you built and when, and what's due next — so the next project starts with the numbers already to hand.