Complete decking material list — joists, deck boards, posts, fixings and concrete — from the deck dimensions.
Enter the deck length and width, the board width and the joist spacing. The tool produces a full material list — joists, decking boards (timber or composite), support posts on a grid, the concrete for setting those posts, and an approximate screw count. Add joist hangers, a ledger board (the board bolted to the house) and post anchors to suit your design.
| Part | Typical |
|---|---|
| Joist spacing | 16 in / 400 mm on-centre |
| Post grid | ≈ 5 ft / 1.5 m |
| Board gap | 3–6 mm (1/8–1/4 in) |
| Waste allowance | 10% (more for diagonal boards) |
A 12 ft × 10 ft deck needs roughly 11 joists across the 10 ft span, about 25 rows of decking, 4–6 support posts and 2 screws at every board-to-joist crossing. That works out to several hundred deck screws — always buy a box extra.
Tip: build the frame level and square first (check the diagonals match), then lay boards; a 5 mm gap lets the timber drain and breathe.
For most timber decking, joists at 400 mm centres are standard. Reduce to 300 mm if you lay boards diagonally or use thinner boards.
Plan for two screws at every point a board crosses a joist. Our estimate uses that rule — buy a little extra to be safe.
As a guide, set posts in holes about 600 mm deep with roughly 0.03 m³ of concrete each, deeper for tall or raised decks.
For most garden decks close to the ground, 150 × 47 mm (6 × 2 in) joists at 400 mm centres are typical. Longer spans or raised decks need deeper joists — check a span table.
Yes, allow about 10% for cuts and the occasional damaged board — more for diagonal or herringbone patterns.
