Offcut WorksDecking clips and screws calculator
Work out how many hidden clips, starter clips and screws your deck needs, and compare them with face screwing.
Two ways to fix boards
Hidden clips sit in a groove along the side of the board and are screwed to the joist, so no screws show on the surface. The clip sets the gap between boards. Face screws go through the board into the joist, with two at each joist, and are the usual method for timber. This page counts both so you can compare them.
How the counts are worked out
Where a row of boards crosses a joist, it needs one clip or two screws. So clips between boards = (rows − 1) × joists, plus 5% spare. A starter clip goes on each joist along the first board, and the last board is face-screwed with two screws per joist. Screws for clips = one per clip.
Face screws = rows × joists × 2, plus 10% spare.
The per-square-metre figure is 1 ÷ (board pitch × joist spacing). For a 145 mm pitch at 300 mm centres that is about 23 clips per square metre, and 17 at 400 mm centres.
Why merchant tables can differ
One merchant's table gives 20 clips per square metre at 300 mm centres and 15 at 400 mm. These figures are lower than the geometry above for a 140 mm board with a 5 mm gap, which suggests the table assumes a wider board or has been rounded. Both are estimates, so buy a small amount of spare either way.
Check the fixings for your boards
- Use the clips made for your board profile. Groove shapes differ between ranges.
- Check the screw type and length. Board makers specify the material, length and head type.
- Allow for the clip gap. The gap you enter here should be the gap the clip creates.
- Count boxes, not single clips. Enter the pack sizes to see how many boxes to buy.
Questions
How many decking clips do I need per square metre?
It depends on board width, gap and joist spacing. As a guide, about 23 per square metre for 140 mm boards with a 5 mm gap at 300 mm centres, and about 17 at 400 mm centres.
Do I need starter clips as well?
Hidden-clip systems usually use starter clips along the first board and face screws for the last. The calculator includes both.
How many screws per board?
For face screwing, two screws per board at each joist is the usual method. Check your board maker's guide.
Can I use the same clip for different gaps?
Each clip creates one gap, such as about 6 mm for a T-clip or about 3 mm for an S-type clip, according to one retailer. Use the clip your board maker specifies.
Where the defaults come from
- Deckorum, composite decking clips. T-clips giving a 6 mm gap, 3 mm S-type clips, and a table of clips per square metre.
- BM Steel, how to fit composite decking. Joists at 400 mm centres and one T-clip per joist.
- HD Deck Pro fitting guide (PDF). Joists no more than 300 mm apart, a clip and screw on every joist, and a 5 to 7 mm gap that depends on temperature.
- eDecks composite decking installation guide (PDF). Joists at 300 mm centres, hidden clips, and a 5 mm gap against solid structures.
- The 10% spare on screws and 5% on clips are our own allowances.
- The starter clip and last-row screw counts follow the hidden-clip method described in the guides we checked, but systems differ.