How many decking boards do I need per square metre?

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.

What gap should I leave between decking boards?

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.

How many screws do I need for decking?

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.

What is the standard decking board length in the UK?

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.

WoodCalcs

Decking Board Calculator — Boards, Screws & Cost

Calculate the number of decking boards, screws, and cost for your deck project.

Board Type

Deck Length

Direction boards run along

Deck Width

Direction boards span across

Board Length

Length of each board

Gap Between Boards

Include 10% wastage

Recommended for cuts and offcuts

Price per Board (optional)

Enter your supplier price for a cost estimate

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

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Last updated: February 2026

All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.