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Decking Calculator

Work out exactly how many boards, joists and screws you need — and get a 2026 material cost estimate.

Calculate Decking Materials

Enter your deck dimensions and board type to get your materials list and cost estimate.

The longest side of your deck area
The shorter side — boards are laid across this direction

Your Decking Materials

Deck Area
—
m²
Boards Needed
—
inc. 10% wastage
Joists Needed
—
at 400mm centres
Screw Boxes
—
boxes of 200
Est. Total Cost
—
materials only

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Where to Buy Decking Materials

Compare prices at the UK's leading retailers before committing to your boards and subframe materials.

RetailerWhat to BuyWhy We Recommend
B&Q Treated softwood boards, composite decking, joists Huge decking range, easy returns, click & collect nationwide
Wickes Hardwood decking, frame timber, post mix Trade-quality timber at competitive prices, delivery available
Amazon UK Decking screws, decking oil & stain, joist hangers Best prices on fixings and finishing products, fast Prime delivery

UK Decking Costs Reference (2026)

Different board types vary significantly in price, lifespan and maintenance requirements. Use this table as a quick reference when planning your project.

Board Type Price per Metre (2026) Typical Lifespan Maintenance
Treated Softwood£3.5010–15 yearsAnnual oil/stain + cleaning
Composite£8.0025–30 yearsOccasional wash only
Hardwood (Balau)£12.0025–40 yearsAnnual oil recommended

Note: Prices are approximate 2026 trade/retail averages. Costs vary by region, supplier, and board profile. Always get at least 3 quotes before purchasing in bulk.

How to Use This Decking Calculator

Step 1: Measure the Deck Length

Measure the longest side of the area where you want to build your deck. This is typically the dimension running along the back of your house. Measure in metres — if you only have feet, divide by 3.281 to convert.

Step 2: Measure the Deck Width

Measure how far the deck will project from the house (or the shorter side of your deck area). The boards will be laid across this direction. A typical garden deck is 2.5–4 metres wide.

Step 3: Choose Your Board Type

Treated softwood is the most affordable option and widely available at UK builders' merchants. Composite decking costs more upfront but needs almost no maintenance. Hardwood (Balau) is premium — extremely durable but the most expensive.

Step 4: Include or Exclude Joists

If you are building a new deck from scratch, select "Yes" to include the joist subframe in the calculation. If you are replacing boards on an existing frame, select "No" to calculate boards and screws only.

Frequently Asked Questions

How many decking boards do I need per square metre?
The number of decking boards per square metre depends on the board width and length. Standard 145mm-wide boards at 3.6m long cover approximately 0.52 m² per board. As a rough guide, you need around 2 boards per m² for standard softwood or composite, though this varies with board dimensions and the amount of wastage from cuts.
Do I need planning permission for decking in the UK?
In most cases, garden decking is classed as permitted development and does not require planning permission in England and Wales. However, you will need permission if the decking is more than 300mm above ground level, covers more than 50% of the garden area, or is in a conservation area, listed building or front garden. Always check with your local planning authority if in doubt.
How far apart should decking joists be?
Decking joists should be spaced at 400mm centres (centre to centre) for standard timber and composite boards. This provides adequate support and prevents boards from flexing underfoot. For diagonal decking patterns, reduce spacing to 300mm centres. Always check the board manufacturer's recommendations as some composite boards may require closer joist spacing.
Is composite decking better than wood?
Composite decking costs more upfront (around £8 per metre vs £3.50 for treated softwood) but requires virtually no maintenance — no annual oiling, staining or sanding. It typically lasts 25–30 years compared to 10–15 years for softwood. Hardwood (such as Balau) lasts 25+ years but needs occasional oiling. The best choice depends on your budget and how much maintenance you are willing to do.
How long does decking last in the UK?
Treated softwood decking typically lasts 10–15 years with regular maintenance (annual cleaning and re-oiling/staining). Hardwood decking such as Balau can last 25–40 years. Composite decking generally lasts 25–30 years with minimal upkeep. The UK climate — with frequent rain and frost — means proper drainage, ventilation underneath, and regular cleaning are essential to maximise the lifespan of any deck.
What is the best time of year to build a deck in the UK?
The best time to build a deck in the UK is late spring through early autumn (April to September). Dry weather makes groundwork easier and allows concrete footings to cure properly. Avoid building during winter as frozen or waterlogged ground makes levelling difficult and timber is more likely to warp if installed wet. Most suppliers also have better stock availability in spring.

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