Decking Calculator
Work out how many decking boards you'll need for your project. Enter your deck dimensions, pick your board type, and we'll do the maths.
1 Your project
Tip: for L-shaped or complex decks, split the area into rectangles, work out each section, and add them together. Boards are calculated to run along the length of your deck.
Which board should I choose?
- Softwood decking is a natural timber option, typically pressure-treated for outdoor use. It's cost-effective and traditional in appearance, but requires periodic staining or oiling to maintain its look.
- Composite decking is made from a blend of wood fibres and recycled plastic. It's lower maintenance, fade and stain-resistant, and tends to have a longer lifespan than softwood.
Things to consider
- Budget: softwood is generally more affordable up front, while composite is a higher initial spend offset by lower long-term upkeep.
- Appearance: softwood offers natural variation in grain; composite gives a more consistent uniform finish.
- Maintenance: softwood needs annual treatment; composite typically just needs a wash down.
- Slip resistance: our composite range includes non-slip technology, ideal for wet or shaded areas.
Softwood decking explained
- Board size: 32 x 125mm with a coverage width of 130mm (125mm board + 5mm expansion gap).
- Lengths: available in 3.0m, 3.6m, 4.2m and 4.8m.
- Finish: reversible boards with grooved and smooth sides for design flexibility.
- Treatment: pressure-treated for ground contact and weather resistance.
Composite decking explained
- HD Deck Dual (22.5 × 143mm): coverage width of 148mm including the 5mm expansion gap. Dual-sided board with grooved and smooth finish.
- HD Deck X (23 × 138mm): coverage width of 143mm including the 5mm expansion gap. Premium board with deep grain texture.
- Length: both ranges supplied in 3.6m boards.
- Fitting: uses hidden clip systems for a clean, screw-free top surface. Clips and starter clips sold separately.
- Lifespan: typically 25+ years with minimal maintenance, resistant to rot, fading and staining.
Important - please read before ordering
This is a guide only. The figures shown are based on the following assumptions:
- Softwood boards: 125mm wide with a 5mm expansion gap (130mm effective coverage per board).
- HD Deck Dual composite: 143mm wide with a 5mm expansion gap (148mm effective coverage per board).
- HD Deck X composite: 138mm wide with a 5mm expansion gap (143mm effective coverage per board).
- Calculation method: rows across the deck width are calculated first (rounded up), then the number of board lengths needed to cover each row is calculated (rounded up). Boards are assumed to run along the length of the deck.
- Waste allowance: selected percentage is added to the base board count to cover cutting, offcuts and breakages, then rounded up to the nearest whole board.
- Rectangular deck: calculation assumes a square or rectangular deck shape with no angled cuts.
For complex deck shapes (curves, angles, multiple levels), the actual quantity required may differ. We recommend increasing your waste allowance for non-rectangular decks. This calculator covers boards only - you'll also need joists, fixings (screws or composite clips), and any edging or trim. For a precise material list, please contact our trade team.