Quickly estimate the amount of decking you need with our easy-to-use Decking Calculator. Get precise results in both square and lineal metres delivered directly to your email. Please remember to add 10% wastage to your calculation for offcuts etc.
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To figure out how much decking timber you need, start by measuring the total area of your deck in square metres (length × width). From there, you’ll want to choose your decking board profile — the width of the board plays a big role in how many boards you’ll need. You’ll also need to account for board spacing (typically 5–8mm between boards) and layout (e.g. diagonal vs straight can change the quantity slightly). It’s best practice to add 10% extra for wastage due to offcuts and human error.
👉 Need help double-checking your quantities? Our team can talk you through the right profile and coverage rates based on your plans. Contact us here.
Square metres (m²) refer to the total surface area you’re covering, think of it like the footprint of your deck. Linear metres (lm), on the other hand, represent the combined length of all decking boards needed. You’ll often buy timber in linear metres because that reflects how much board is used, regardless of width. For example, if you’re using 90mm-wide boards, you’ll need more linear metres to cover a space than if you’re using 130mm-wide boards. Understanding both units helps you estimate costs and avoid under-ordering. Our calculator automatically works this out based on your board profile.
New Zealand’s climate varies significantly across regions, so selecting the right timber is essential. Durable hardwoods such as Spotted Gum, Royal Reds (a mix of Red Mahogany and Turpentine), and Grey Box are popular choices due to their Class 1 durability rating—lasting over 40 years. In contrast, Kwila, for example, is a Class 2 timber with a durability range of 15–40 years.
In wetter areas, high timber durability and proper sealing are especially important, while in drier regions, choosing a timber that offers good dimensional stability may be a higher priority. Always refer to the durability rating when making your selection.
Be cautious about relying solely on FSC certification. For instance, Kwila (Intsia bijuga) is listed on the IUCN Red List of Threatened Species—raising serious questions about the sustainability of its sourcing. We urge you to avoid supporting the import of tropical rainforest timbers like Kwila, Garapa, Vitex, and Purpleheart. Your choices can make a difference—please help protect these vulnerable ecosystems.
While basic calculators are helpful for flat, single-level decks, raised or multi-level decks often require extra structural components like joists, bearers, posts, and stair treads. These don’t factor into the basic surface area calculation. If your project includes elevation changes or structural complexity, it’s best to speak with a builder or LMA Timber directly to get a more comprehensive material list and pricing estimate.
In NZ, you don’t need building consent for a deck that’s under 1.5 metres high, as long as it’s not part of a pool barrier or other restricted feature. However, it must still be built to code. Anything over 1.5 metres high or attached to a dwelling may require consent. Always check with your local council before starting your project, especially if you’re building near boundaries or on sloped land.
Please refer to our decking install guide which can be found in our downloads section. For boards up to 70mm wide use a minimum gap of 3mm and for boards over 70mm wide use a minimum gap of 5mm. Close to ground decks (under 400mm)require a 6mm minimum gap between boards regardless of board width.
