Work out deck boards, joists, posts, concrete, screws, fascia, steps, balustrade and a realistic materials cost. This is designed as a practical planning tool for rectangular timber decking projects in the UK.
Use this to get a sensible guide before ordering materials or pricing a job. You can also switch the optional extras on and off.
Good for early estimates, rough pricing and comparing deck sizes before ordering materials.
Helps you decide how many boards, joists and posts you are likely to need before layout is finalised.
You can edit the default prices to better reflect your local timber merchant or your usual supplier rates.
A clean breakdown you can use for materials planning, quoting or turning into a shopping list.
These answer the common practical questions around materials, layout, joist spacing, waste, posts, costs and how accurate a decking calculator really is.
This calculator is designed to give a solid guide for a standard rectangular timber deck. It works well for early planning, pricing and shopping lists, but final quantities can change once the full frame design, picture framing, stairs, rails, double joists or awkward cut-outs are confirmed.
Yes. You can choose your own waste percentage. A small, straightforward deck may only need around 5%, while more cut-heavy layouts or decks with features and borders often justify 10% to 15%.
For many timber decks, 400mm centres is a common starting point and gives a solid feel underfoot. Some thinner boards or higher-spec builds may benefit from 300mm centres, while wider spacings can feel more flexible depending on the board profile and quality.
It can still help with the basic layout size, but it is mainly set up around timber decking assumptions. Composite systems often have their own joist spacing, clip systems, expansion requirements and board coverage, so the final quantities can differ.
The calculator works out how many rows of boards are needed across the deck using the actual board face width plus the expansion or drainage gap between each board. Wider boards or tighter gaps usually reduce the number of rows required.
Posts are estimated around the perimeter using your chosen maximum post spacing. It is a sensible guide for planning, but the real number may change depending on the height of the deck, beam layout, stair positions, load requirements and whether the deck is freestanding or attached.
Start with the deck area, then check the calculated number of boards, joists and posts, and finally add a realistic waste allowance. Ordering exactly the theoretical minimum is rarely a good idea because cuts, defects and layout decisions usually increase the requirement slightly.
The calculator shows both a materials-only figure and a separate supply-and-fit guide. The labour side is based on a simple per-square-metre rate so you can change it to reflect your own market, typical spec or local install rates.
Yes, it works well as a first-pass quoting tool. It is especially useful when a customer wants a rough figure quickly. For a proper final quote, it is still best to confirm the exact frame design, steps, rails, access, waste removal and site prep.
No, not every deck uses fascia in the same way, but it often gives the perimeter a much cleaner finished look. Fascia can also help hide the edge of the frame and the ends of boards, especially on raised decks.
This calculator estimates screws using two screws per board at each joist crossing. That gives a sensible planning figure for traditional face-fixed decking, though hidden fixing systems and manufacturer-specific details may change the actual requirement.
It is a useful comparison figure, especially when looking at different deck sizes or spec levels. It becomes less exact on very small decks or more complex builds because extras like steps, balustrade, groundwork and edge details can have a bigger effect on the final price.
