Decking Cost Calculator

Compare softwood, hardwood and composite decking costs for a worked project comparison and purchasing advice.

How to budget for decking

A usable decking budget includes the visible boards and the hidden structure: posts, bearers, joists, fixings and suitable foundations. Measure the finished footprint, decide the board direction, then sketch the frame before ordering.

Use the calculator for a quantity-led starting point, then check it against the chosen manufacturer's technical information and a supplier quote. Product dimensions, coverage and pack sizes change, and a low advertised unit rate can be offset by delivery, minimum orders or accessories. Keep the measurements, quantity calculation and cost assumptions together so they can be updated without remeasuring the project.

Typical UK decking prices

The figures below are illustrative UK ranges as at September 2026, including VAT where normally charged. Supply-only means the main named material and does not automatically include preparation, delivery, accessories or waste. Supplied-and-fitted ranges are broad consumer budgeting figures, not quotations; London, difficult access and unusually small jobs can cost more.

Prices are shown per m² or board as appropriate. Compare like with like: clarify VAT, delivery, removal of old material, preparation, finishing and guarantees. A contractor rate may include several of these, while a retailer's headline price generally does not. Obtain current local prices before ordering or agreeing work.

Worked example: calculation step by step

Consider a 4m × 3m rectangular deck, an area of 12m². With boards running along the 4m side and an effective board width including gap of 144mm, the deck needs 3 ÷ 0.144 = 20.84 board rows. Round up to 21. Each row is 4m, giving 84 linear metres.

Add 5% for square cuts: 84 × 1.05 = 88.2 linear metres. Using 3.6m boards means 88.2 ÷ 3.6 = 24.5, so buy 25 boards. At £14.50 each, boards cost £362.50. Add a £210 frame allowance and £65 for structural screws, clips and feet: the indicative DIY material total is £637.50.

If professionally fitted softwood is quoted at £125 per m², the broad comparison is 12 × £125 = £1,500. Steps, balustrades, difficult levels and spoil removal could sit outside that rate, so ask for an itemised scope.

What drives the cost?

• Softwood, hardwood or composite board choice. Ask whether this is included in a price and what assumption has been made. A change here can affect material quantity, labour time and the supporting work, so it deserves its own budget line rather than being hidden in a general contingency.
• Height, spans and complexity of the sub-frame. Ask whether this is included in a price and what assumption has been made. A change here can affect material quantity, labour time and the supporting work, so it deserves its own budget line rather than being hidden in a general contingency.
• Steps, curves, picture framing and balustrades. Ask whether this is included in a price and what assumption has been made. A change here can affect material quantity, labour time and the supporting work, so it deserves its own budget line rather than being hidden in a general contingency.
• Ground preparation and foundation method. Ask whether this is included in a price and what assumption has been made. A change here can affect material quantity, labour time and the supporting work, so it deserves its own budget line rather than being hidden in a general contingency.
• Site access and local labour rates. Ask whether this is included in a price and what assumption has been made. A change here can affect material quantity, labour time and the supporting work, so it deserves its own budget line rather than being hidden in a general contingency.

Project scale also changes the unit cost. A contractor still has travel, setup and administration on a small job, while larger orders may attract delivery efficiencies. Geography matters too: labour and parking are commonly higher in London and parts of the South East, while remote deliveries can carry their own premium. Seasonal demand may change lead times even where the quoted rate is stable.

Wastage allowance

Allow about 5% on a simple rectangular deck with boards laid square. Use 8–10% where boards are laid diagonally, borders create mitres, or short stock lengths lead to many joins. Complex curves may need 12–15%. Waste covers end trimming, defects and cuts that cannot be reused while keeping staggered joins structurally sound.

Apply waste to quantity before rounding to whole packs, boards, bags or rolls. Rounding first and then adding a percentage can either overbuy or leave an unusable fraction. If unopened stock is returnable, check the return window and batch restrictions. Do not assume every surplus item can be returned: special orders, mixed products and cut lengths are commonly excluded.

Measure and plan before buying

Draw the area and label every dimension instead of relying on one length and width from memory. Split L-shaped or stepped spaces into rectangles, calculate each one, and add the results. Measure in the same unit throughout. Recheck the narrowest access, floor levels, corners and fixed obstacles because these can determine product size, installation sequence or whether specialist equipment is needed.

Read the technical sheet before substituting one product for another. Two items sold for the same purpose may have different coverage, fitting centres, thicknesses or base requirements. Check compatibility between the main material and its fixings, adhesive, membrane or substrate. Manufacturer instructions normally take priority over a general calculator and may be required to preserve a warranty.

DIY budget versus a fitted quote

A DIY total should include consumables, personal protective equipment, tool hire, delivery and disposal, not only the finish material. It is sensible to keep a separate contingency of around 5–10% of the complete budget for discoveries and price movement. That contingency is different from material waste: wastage buys enough physical product, while contingency protects the cash budget.

For professional work, seek an itemised written quote. It should identify preparation, material specification, quantity, waste ownership, access assumptions, protection, cleanup, disposal, VAT, payment stages and guarantee. Ask what would count as a variation. Comparing itemised scopes is more reliable than choosing the lowest total where important work may be omitted.

Using this estimate responsibly

The result is a planning estimate, not a structural design or site survey. Hidden defects, moisture, unsuitable ground and regulated work cannot be diagnosed from dimensions alone. Confirm structural, fire, electrical, ventilation and planning requirements with a suitably competent person where they apply. Stop and investigate if the existing surface is damp, unstable or contaminated.

Save the exact product details used in the calculation, including pack coverage and unit price. When a quote or retailer price changes, update that input rather than altering the measured area. This makes the estimate auditable and helps distinguish a genuine price change from a quantity error.

Frequently asked questions