Decking Calculator UK
Estimate the exact number of deck boards, joists, and total project cost for your garden. Supports softwood, hardwood, and composite materials.
Decking Material Estimator
Calculate boards, subframe, and total costs
Total length of the decking area
Total width of the decking area
Standard is 144mm (90mm x 90mm)
Standard lengths: 3.6m or 4.8m
Leave 3-5mm for wood expansion
Add 10% for cuts and mistakes
Choose your preferred decking type
Centre-to-centre joist spacing
Decking Estimate
Boards, joists, and total project breakdown
Enter your deck dimensions and material preferences, then click Calculate to see your material requirements and estimated costs.
Average UK Decking Costs
Typical material and installation prices for garden decking in the UK based on current market averages.
| Material Type | Material Cost (per m²) | Supply & Fit (per m²) |
|---|---|---|
| Softwood (Treated) | £25 – £40 | £120 – £160 |
| Hardwood (Premium) | £60 – £100 | £160 – £220 |
| Composite (Standard) | £60 – £90 | £160 – £210 |
| Composite (Premium) | £90 – £120+ | £190 – £250+ |
UK Decking FAQ
Everything you need to know about planning, materials, and building a deck in the UK.
To calculate decking materials, first measure the total area in square metres (length × width). Next, determine the width of your deck boards plus the expansion gap (usually 3-5mm). Divide the total width of your deck by the effective board width to find how many boards per row. Then, divide the total length by the board length to find the number of rows. Multiply these together and add 10% for waste and cuts.
In the UK, the standard centre spacing for decking joists is 400mm (40cm) for standard softwood and composite boards. If you are using thinner 22mm boards or heavy-duty composite, you may need to reduce the spacing to 300mm to prevent sagging and ensure structural integrity.
The cost of decking in the UK varies by material. Softwood decking typically costs £25 to £40 per square metre for materials. Hardwood ranges from £60 to £100 per m². Composite decking, which requires less maintenance, costs between £60 and £120 per m². If hiring a professional, expect to pay an additional £100 to £150 per m² for labour and subframe materials.
Yes, absolutely. You must leave a gap of at least 3mm to 5mm between decking boards. Wood is a natural material that expands and contracts with changes in moisture and temperature. Without an expansion gap, the boards will buckle, warp, or crack during the summer months. Composite decking also requires a gap for thermal expansion and drainage.
Composite decking is more durable, requires virtually no maintenance (no sanding or staining), and doesn’t rot or splinter. However, it is significantly more expensive upfront than softwood. Softwood is cheaper and looks natural but requires annual cleaning and staining to prevent rot and slipping. Hardwood offers a middle ground with high durability and a premium natural look.
In the UK, you generally do not need planning permission for standard garden decking as long as it is less than 30cm above ground level and covers no more than 50% of your garden area. If the decking is higher than 30cm, or attached to a listed building or in a conservation area, you will likely need to apply for planning permission.