Screws are tiny but the right count and type make the difference between a deck that lasts 20 years and one that wobbles in two.
Plan for 25–30 screws per m² of deck. That's 2 screws into each joist for every board crossing.
Per board-on-joist crossing you put 2 screws (one near each long edge of the board).
On a deck with 14 cm boards and joists every 60 cm, that's about 8–9 crossings per m² – so 16–18 screws from the board grid. Add a bit for end-cuts, picture-frame edges and joins and you land on 25–30 per m².
Buy 5–10 % extra – some always end up on the floor or get binned when the head strips.
20 m² × 27 screws/m² = roughly 540 screws. Boxes come in 250s and 500s, so grab two 250-packs or a 500-pack plus a small spare.
The calculator works out screws alongside boards and joists – so you only shop once.
Stainless A2 for normal conditions, A4 if you're near the coast. Coated carbon-steel decking screws also work well as long as they're never in salt spray.
Rule of thumb: 2 × the board thickness, with a 50 mm minimum. For a 25 mm board, use 60 mm screws.
Yes for hardwood (larch, ipe, composites). It stops the board splitting and gives a cleaner head.
Yes, just below the surface so water sheds. Most decking screws are self-countersinking.
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