The formula
Rows = deck width ÷ (board width + gap), rounded up. Board metres = rows × deck length. Stock boards = board metres ÷ stock length, plus allowance, rounded up. Joists = ceil(deck length ÷ spacing) + 1.
Garden • UK CALCULATOR
Decking Calculator UK
Estimate surface decking boards, joist linear metres and screw packs for a simple rectangular deck. Set the stock board length, width and spacing you plan to use.
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Your estimate starts here
Enter your measurements and calculate to see materials, quantities and an optional price estimate.
GOOD TO KNOW
How this calculator works
Worked example
A 4 × 3 m deck with 145 mm boards and 5 mm gaps needs roughly 20 board rows across the 3 m width.
Check before ordering
This is a preliminary surface and simple joist quantity estimate, not a structural frame design or cutting plan. It excludes bearers, supports, anchors, rails and stairs. Board offcut reuse and joint positions matter; seek proper guidance for elevated or load-bearing structures.