Decking Board Calculator
Instantly work out how many decking boards, linear metres, and materials you need for your deck based on its size and your board dimensions. Accurate for timber and composite decking projects.
Calculate Your Decking Boards
Enter your deck dimensions and board specifications below to get an instant, accurate estimate of how many boards you’ll need.
Decking Calculator
Enter your deck size to see how many boards you need
Boards are assumed to run along the length of the deck
4-6mm is standard for timber, 5-8mm for composite decking
Extra material for cuts, offcuts, and mistakes
Boards Required
Calculated from your deck size and board dimensions
Standard Decking Board Sizes
Common decking board dimensions used in the UK. Use this to double-check the specification of the boards you’re planning to buy.
| Board Width | Board Length | Coverage per Board | Common Use |
|---|---|---|---|
| 90mm | 2.4m | 0.216 m² | Narrow-profile timber decking |
| 120mm | 3.6m | 0.432 m² | Standard softwood decking |
| 140mm | 2.4m | 0.336 m² | Composite decking boards |
| 150mm | 4.8m | 0.72 m² | Wide-format hardwood decking |
Decking Calculator FAQ
Everything you need to know about calculating materials for your decking project.
To work out how many decking boards you need, divide your deck width by the board width plus the gap between boards to get the number of rows, then multiply by your deck length to get the total linear metres. Divide that by the length of a single board to get the number of boards, and add 5 to 10 percent extra for cutting and wastage.
A gap of 4mm to 6mm is standard for timber decking to allow for drainage and natural expansion. Composite decking often requires a slightly wider gap, typically 5mm to 8mm, so always check the manufacturer’s guidance.
Most tradespeople recommend adding 5 to 10 percent extra decking material to account for cutting, offcuts, and mistakes. Complex layouts with diagonal cuts or multiple angles may need up to 15 percent extra.
To calculate the area of your deck, multiply the length by the width in metres. For example, a deck 5m long and 4m wide has an area of 20 square metres, which forms the basis for working out board and joist quantities.