You typically need 35–40 deck screws per m² — about 3–4 screws per square foot. The number comes from the basic rule of two screws per board at every joist: with common 120 mm (4.7 in) boards and standard joist spacing, most projects land in this range. A 20 m² (about 215 sq ft) deck therefore means roughly 700–800 screws before any buffer.
Below you can see how the number varies with joist spacing and board width, which screws to choose, and how to calculate the total for your own project.
Screws per m² by joist spacing and board width
The screw count is driven by how many board rows you have per meter and how many joists each board crosses. The table shows the theoretical need with a 5 mm (3/16 in) gap between boards, rounded up and without any buffer:
| Board width | 60 cm (24 in) spacing | 40 cm (16 in) spacing |
|---|---|---|
| 95 mm | approx. 34 screws/m² | approx. 50 screws/m² |
| 120 mm | approx. 27 screws/m² | approx. 40 screws/m² |
| 145 mm | approx. 23 screws/m² | approx. 34 screws/m² |
Standard joist spacing is 60 cm (24 in) on center, while thin boards, diagonal installation, or composite decking often require 40 cm (16 in). Read more about that choice in what joist spacing should you use for a deck.
Once you round up to full boxes and add some allowance for waste, the rule of thumb of 35–40 screws per m² holds up well for the most common combinations. With wide boards on 60 cm spacing you can get away with slightly less, but it is rarely wise to plan right at the limit.
Worked example
- Area: 24 m² (about 260 sq ft)
- Screws per m²: 35
- Total: 24 × 35 = 840 screws
Add around 10 % buffer for dropped screws, rejects, and future repairs, then round up to the nearest box size. That keeps you on the safe side without buying blindly.
Choose the right type of screw
The screws have to survive weather, moisture, and wood movement for many years:
- Stainless steel screws (A2/A4) — the first choice outdoors. A4 (marine grade) is recommended near the coast and for hardwoods.
- Galvanized or coated screws — cheaper, but less resistant to corrosion over time.
- Deck screws with a cutting/reaming head — countersink neatly into the board without pre-drilling and reduce the risk of splitting.
Choose a length of at least 2.5 times the board thickness. For 28 mm (1 1/8 in) boards that means screws of around 70 mm (2 3/4 in). If you want to avoid visible screw heads entirely, hidden fastening with clips is an alternative.
How to use the calculator
The calculator on this page works out the screw count from your deck area and board width, using standard assumptions for joist spacing and gap. You get a quick estimate of both decking quantity and screw count — a handy shopping list before you head to the lumber yard. For the board side of the estimate, see how to estimate deck boards with a calculator.
If you want to understand the fastening pattern behind the numbers, the deck screw spacing guide shows how to count screws per board.
Frequently asked questions
How many screws do I need per m² of decking?
Plan for 35–40 screws per m² (3–4 per sq ft) for standard deck boards with face fastening. The number is based on two screws per board at every joist and varies with board width and joist spacing.
How many screws per deck board?
Two screws every time the board crosses a joist. A board crossing 10 joists therefore needs about 20 screws.
How long should deck screws be?
At least 2.5 times the board thickness. For 28 mm (1 1/8 in) deck boards, roughly 70 mm (2 3/4 in) screws are right; for 21 mm (about 7/8 in) boards, 55–60 mm (around 2 1/4 in) is enough.
Should I buy extra screws?
Yes, add around 10 % buffer. Dropped screws, rejects, and later repairs are completely normal, and a spare box of deck screws rarely goes unused.
Do I need to pre-drill?
With self-countersinking deck screws, pre-drilling is rarely necessary in pressure-treated softwood, but do pre-drill near board ends and always in hardwood. Check the screw manufacturer’s recommendation.