Decking Calculator NZ

This calculator works out the timber you need to build a deck, so you can order the right amount of decking boards and joists before you start. Enter your deck length and width in metres, the width of the boards you plan to use in millimetres, the gap you want between boards, the length of the boards you intend to buy, and your joist spacing in millimetres. From these figures it returns the rows of decking needed to cover the width, the total lineal metres of decking required, the number of boards to buy once board length is accounted for, and the number of joists needed to support the deck at your chosen spacing. It works by dividing the deck width by the board width plus the gap to get the rows, multiplying by the deck length for the lineal metres, then dividing by your board length for the boards, while joists come from the deck length divided by the spacing, plus one. Use it before ordering timber so you buy the right quantity rather than guessing and running short. A gap of 3 to 5 mm between boards is typical for drainage and movement, and joist spacing is usually 400 to 450 mm depending on board thickness. This is a materials estimate only, so check span tables and the building code, and add extra for waste and cuts.

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Estimate for boards running the length of the deck. Add a little for waste and cuts.