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Deck screws calculator
How many deck screws do you need? Not a bag guess — the count comes from the real board-to-joist crossings on your deck. Draw the deck once and the fixings appear beside the boards, joists and frame. Free, no sign-up, and nothing is priced until you add your own rates.
The rule in three lines
1. Count the board rows
Deck width divided by the board width plus the gap, rounded up. The gap matters: 5 mm in the UK, 3/16 in in the US.
2. Count the joists
Deck length divided by the joist centres, plus one for the last joist. 16 in centres in the US and Canada, 400 mm in the UK and Ireland.
3. Multiply, then pick the fixing
Rows x joists gives the crossings. Two screws per crossing for face-fixed boards, one clip per crossing for a hidden system.
A worked example
- Deck
- 16 ft x 12 ft, US practice
- Joists at 16 in centres
- 13
- Board rows
- 26
- Board-to-joist crossings
- 338
- Face screws (2 per crossing)
- 676
- Hidden clips instead (1 per crossing)
- 338
Switch the country to the UK and the joist centres drop to 400 mm, so the same deck gets more joists, more crossings and more fixings. The number on screen always says which rule produced it.
Common questions
How many deck screws do I need?
Count the crossings, not the area. Every board crosses every joist once, and a face-fixed board takes two screws at each crossing. So screws = boards x joists x 2. A 16 ft x 12 ft deck with 16 in joist centres has 13 joists and 26 board rows, which is 338 crossings and 676 screws before any waste.
What about hidden clips instead?
Hidden fasteners sit one per crossing, not two, so the same deck needs 338 clips. Composite boards are usually clipped; treated softwood is usually face-screwed.
How many spare should I buy?
Screws snap, heads strip and cuts change the board layout, so buying a box above the counted number is normal. The tool gives you the counted figure; the spare is your call, not a hidden multiplier we add for you.
Does joist spacing change the screw count?
Yes, directly. UK practice at 400 mm centres puts more joists under the same deck than 16 in centres, so more crossings and more fixings. Pick the country and the count follows that practice.
What about the frame fixings?
They are counted separately: joist hangers, structural screws or bolts into the ledger and posts, and the concrete for the footings. They are listed as their own lines so nothing is folded into a vague 'fixings' number.
Fixings are one line of the list
Draw the deck once and the boards by buying length, joists, beams, posts, footings, stairs, railing and fixings are calculated together. The complete pack provides the order-ready PDF and CSV.
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