Decking Calculator
Work out exactly how many boards, joists, and fixings you need — plus a realistic total cost estimate for timber, hardwood, or composite decking, including labour.
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How decking costs are calculated
Decking projects involve more materials than most people expect. Beyond the boards themselves, you need joists, post pads or bearers, fixings, and potentially ledger boards, joist hangers, and gravel boards if the deck is close to the ground. This calculator gives you a realistic all-in figure for 2026 UK prices.
Labour rates for decking in the UK
A competent carpenter or groundwork contractor charges £50–£80 per square metre to install decking in the UK. This calculator uses £65/m² as a mid-range figure. Elevated decks cost more — add around £20/m² for extra post and beam work. In London, South East England, and major cities, expect prices toward the top of the range.
Choosing your decking material
Pressure-treated softwood (usually pine or spruce) is the most widely installed decking in the UK. At around £18/m² for boards, it is affordable, widely available from builders' merchants, and works well in most UK climates when maintained properly. Annual oiling extends its life substantially.
Hardwood decking — bangkirai, ipe, and cumaru are the most common species — costs significantly more but delivers a premium finish and far greater durability. Ipe in particular has a Class 1 durability rating and does not need regular treatment, making it the preferred choice for high-end garden rooms and commercial installations.
Composite decking is the fastest-growing option in the UK market. Made from a mixture of recycled wood fibre and plastic, it does not rot, splinter, or fade significantly. The main brands — Trex, Millboard, Cladco, and Eva-Tech — all offer 25-year warranties. Costs are higher upfront, but zero ongoing maintenance often makes it more economical over a 20-year period.
Waste allowance and board counts
Always buy more boards than the bare calculation suggests. Cutting to length creates off-cuts, and some boards will have knots or defects that need rejecting. This calculator applies a 10–12% waste allowance (8% for composite, which tends to have less waste due to consistent quality).
Decking and building regulations
Elevated decking more than 300mm above ground may require building regulations approval, particularly if it is attached to the house. A structural engineer's assessment is advisable for any deck over 600mm high. Even where planning permission is not needed, your work should still comply with Part K (Protection from falling) of the Building Regulations if the deck is above ground level.
Quoting for decking jobs
Getting paid fairly for decking work starts with a clear, itemised quote. Break down boards, joists, fixings, post pads, and labour separately so clients understand what they are paying for. Use InvoiceAdept's quote generator to produce professional, branded quotes from your phone or laptop in minutes. Once the job is done, send the invoice directly to your client.
Frequently asked questions
How much does decking cost per square metre in the UK?
Decking costs in the UK typically range from £80 to £200 per square metre fully installed. Pressure-treated softwood sits at the lower end (£80–£120/m²), hardwood such as bangkirai or ipe runs £150–£200/m², and composite decking lands at £180–£250/m². These figures include materials, joists, fixings, and labour.
How many decking boards do I need?
For a standard 4m × 3m deck using 125mm-wide boards with a 5mm gap, you need approximately 23 boards assuming 3.6m standard lengths. This calculator works out the board count automatically based on your deck dimensions, board width, and a 10–12% waste allowance for cuts and off-cuts.
Do I need planning permission for decking in the UK?
Decking under 300mm above ground level and covering less than 50% of the total garden area does not typically need planning permission in England and Wales under permitted development rights. Elevated decking over 300mm high, or any decking attached to a listed building or in a conservation area, usually does require permission. Check with your local planning authority before starting work.
What joist spacing should I use for decking?
For standard softwood decking boards (22–32mm thick), a joist spacing of 400mm is standard and gives a firm, bounce-free deck. For composite and thinner hardwood boards, 300mm centres are safer to prevent flex. This calculator uses 400mm joist centres for all materials as a conservative estimate.
Is composite or timber decking better?
Timber is cheaper upfront but requires annual oiling or staining to maintain its appearance and prevent rot. Pressure-treated softwood is the budget option — it lasts 15–25 years with maintenance. Hardwood lasts 30+ years with minimal care. Composite decking costs more to buy and install, but is virtually maintenance-free and carries 20–25 year warranties from most manufacturers. Over a 25-year period, composite can work out cheaper than repeatedly treating timber.
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