Decking calculator
Work out how many deck boards you need. Enter your deck size and the board dimensions and this calculator gives you the number of boards, plus the joists and screws.
Decking calculator
Enter your measurements in metres. Everything updates as you type, and nothing is sent anywhere.
Boards are laid with a 5mm gap, and 10% is added for waste and cuts. Joists are estimated at 400mm centres, which suits most softwood decking; composite and thinner boards often need 300mm. The joist and screw figures are approximate, since the direction you lay the boards changes the framing.
Common questions
How many deck boards do I need?
It depends on the board size. Work out the deck area, then divide by the coverage of one board, its length times its width plus the gap. This calculator does it for you and adds 10% for waste and cuts.
How far apart should decking joists be?
400mm centres is standard for most softwood decking. Composite boards and thinner timber usually need joists closer together, around 300mm, so check the board maker's guidance.
These are independent guide prices based on typical UK jobs in 2026. Your actual cost depends on your property, spec, access and where you live. Always get at least three written quotes before committing. These quantities are a guide to help you order. Always round up and check with your supplier before buying.