By the MyPlanDIY editorial teamLast updated
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. The count depends mostly on how far apart your joists are.
Two screws at every point where a board crosses a joist. With 140 mm boards that's about 24 screws per m² on 600 mm joists, 32 on 450 mm and 36 on 400 mm (about 16 in) joists. Add 5–10 % extra.
Screws per m² = 2 × (1 ÷ board width in m) × (1 ÷ joist spacing in m). The 2 is one screw near each long edge of the board.
For 140 mm boards: joists at 600 mm → about 24 per m²; at 450 mm → about 32; at 400 mm → about 36; at 300 mm → about 48. The joist spacing your boards need is set by the board manufacturer, so check that before you count.
Buy 5–10 % extra for end cuts, edges and the screws that strip or get lost.
20 m² × 36 screws/m² = 720 screws. Add 5–10 % and aim for roughly 760–790. Decking screws come in boxes of a few hundred, so round up to the next sensible box size and keep the leftovers for repairs.
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.
Keep going with one of these – they pair well with what you just read.
Deck project from start to finish
Step-by-step guide to planning and building a deck. Measuring, materials, budget and mistakes.
Read guide →Deck materials list
What to buy for a deck project: an example materials list covering boards, joists, screws and footings.
Read guide →Deck joist spacing guide
How far apart should deck joists sit? It depends on board type, thickness and load – with clear rules of thumb.
Read guide →Fence calculator
Calculate posts, boards and screws for a simple wooden fence.
Open calculator →Flooring calculator
Calculate packs of laminate or floorboards based on area and waste.
Open calculator →Drywall calculator
Calculate the number of drywall sheets or panels for walls or ceilings.
Open calculator →Create a free account and explore all features with a complete sample project.
No credit card required. Free sample project included.