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Decking Board Calculator — Boards, Screws & Cost
Calculate the number of decking boards, screws, and cost for your deck project.
Recommended for cuts and offcuts
How We Calculate This
This calculator determines the number of decking boards needed based on your deck dimensions, board size, and gap width.
Board count formula
Boards across = ceil(Deck width / (Board width + Gap))
Boards along = ceil(Deck length / Board length)
Total boards = Boards across x Boards along x Wastage factor
Screw count assumes 2 screws per joist crossing at 400mm joist spacing. A 10% wastage allowance covers end cuts and any defective boards.
Frequently Asked Questions
For standard 125mm boards with 5mm gaps, you need approximately 7.7 boards per linear metre of deck width. Per square metre, you need about 8 boards of 1m length. The exact count depends on board width, gap size, and board length.
Leave a 5-8mm gap between timber decking boards to allow for drainage and wood expansion. Composite decking typically needs 5-6mm gaps. In winter when timber is dry, gaps may widen to 8-10mm. Use spacers during installation for consistent gaps.
Use 2 screws per board at each joist crossing. With standard 400mm joist spacing, a 3.6m board crosses approximately 10 joists, needing 20 screws per board. Use stainless steel or coated screws (4.5 x 60mm or 5.0 x 65mm) to prevent corrosion.
UK decking boards are commonly available in 2.4m, 3.0m, 3.6m, and 4.8m lengths. 3.6m is the most popular. Plan your deck dimensions around standard lengths to minimise waste. For larger decks, stagger the board joints over different joists.
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Last updated: February 2026
All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.