Decking calculator
Enter the size of the deck and get the boards, joists, beams, posts, footings, steps, railing and fixings to buy — drawn in 3D so you can see what the numbers describe. Free, no sign-up, and nothing is priced until you add your own rates.
How the quantities are worked out
1. Measure the area
Take the width and the length of the finished deck, not the garden. Work to the outside face of the frame; the calculator adds the board gap for you.
2. Pick the board and the direction
Board width and the gap between boards change how many boards you buy. Composite and softwood come in different widths, so the count changes with the material.
3. Let the frame follow the span
Joist and beam spacing follow the building practice of your country. Composite boards usually need closer joists than softwood, which is where most hand-made lists go wrong.
4. Buy in stock lengths
Boards are sold in fixed lengths. The cut list packs your runs into stock lengths and shows the offcuts, so you order what a merchant actually sells.
Common questions
How many decking boards do I need?
Divide the deck width by the board width plus the gap, then multiply the rows by the deck length and pack that into stock lengths. The calculator does this and shows the offcuts, so you can check the number instead of trusting it.
Does it give me a price?
Only if you enter your own supplier rates. There are no national averages and no invented figures here — a price with someone else's rates in it is the reason so many online numbers come in thousands under the real quotes.
Metres or feet?
Both. Pick your country and switch between metres and feet; the quantities follow that country's building practice.
Is this a structural design?
No. It is a material take-off to plan and price the job. Spans, footings and railings still need checking against local rules and, where needed, building control.
Building for clients?
Save your own rates once and every take-off turns into a quote with your labour, margin and tax, ready to print with your company name on it.
See the plans