Decking Calculator

Boards, joists, posts, screws and clips.

Inputs

Got a bay window or conservatory? Set it out in Setting Out & Levels → Bays & conservatories. It carves the bay footprint out of the paved area and adjusts the wall run, then hands the corrected figures back here.

Decking type

Project location

Length(m)

Width(m)

Deck height(mm)

6 advanced inputs hidden. Switch to Advanced to fine-tune.

Confidencehigh· 78Complexitymedium· 34

Boards required

Order what you need for this job

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Heads-up: Softwood decking uses joist centres at 400 mm, screws into pre-drilled pilot holes, and needs a 150 mm ventilation gap under the deck so it can breathe. Why it matters: Sealed-under decking traps moisture, rots joists, and harbours rats — keep the air moving.

Quantities pre-filled from your calculation (15.0 m²). Partner links — we may earn a small commission if you buy, at no cost to you.

Essentials for this job

Treated softwood decking boards
Building Materials Nationwide
Need ~17 m² for your job
Pressure-treated 28×145 mm boards, 3.6 m / 4.8 m lengths.
Guide price: £25–£45 / m²(~£425–£765 total)
Indicative · reviewed May 2026
See options at Building Materials Nationwide

Quantities include a ~10% waste allowance. Guide prices are indicative UK ranges (materials only, inc. VAT) — always confirm with the supplier before ordering.

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Ad · Some links are sponsored. We may earn a small commission at no extra cost to you. Suppliers are chosen for fit, not commission.

This app provides general UK guidance and material estimates only. It is not legal, planning, engineering or building-control advice. Always confirm requirements with your local planning authority, building control, utility providers, manufacturers or qualified professionals.