UK DIY Cost Calculator
Decking Cost Calculator
Estimate the boards, joists and fixings for a timber or composite deck, and the total material cost. Enter your deck size and board dimensions for a full breakdown.
Your project
Estimate
Estimates are for guidance only. Coverage rates, pack sizes and prices vary by brand — always confirm quantities with your supplier before buying.
Decking is more than just boards
The deck boards are the visible cost, but the frame underneath — joists, bearers and posts — plus the screws and joist feet often add up to as much as the boards themselves. This calculator sizes the boards precisely from your deck dimensions and lets you add a realistic allowance for the frame and fixings so the total reflects the whole job.
Timber vs composite
Softwood decking is cheapest upfront but needs regular treating. Composite costs considerably more per board but skips the annual maintenance, so the right choice depends on how long you'll keep the deck and how much upkeep you're willing to do. Enter the per-board price for whichever you're pricing.
Frequently asked questions
How many decking boards do I need?
It depends on board width and deck size — a 4m x 3m deck with 144mm boards needs roughly 21 boards at 3.6m plus waste. The calculator works out your exact count from the dimensions you enter.
How much does a deck cost to build?
A small softwood deck can cost a few hundred pounds in materials; composite of the same size often costs two to three times more. Add labour if you're not building it yourself.
Why add a frame allowance?
The sub-frame of joists and bearers is essential and easy to forget when pricing. Entering a frame allowance keeps the total honest — for many decks the frame timber and fixings rival the cost of the boards.
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