Decking Calculator NZ
Use this decking calculator to quickly work out how many boards, linear metres and screws you need for your deck in New Zealand.
How to use this decking calculator
Enter your deck length and width in metres. Select your timber profile — 140mm pine is the most common choice for NZ residential decks. Choose your board gap and the length of boards you plan to buy. The calculator works out linear metres, number of boards, screws needed and screw boxes. Switch to Cost Estimate mode to get a material cost breakdown in NZD.
Always add at least 10% for waste. Decking cuts produce offcuts, and boards sometimes have defects. Ordering short is a costly mistake.
NZ timber guide — which decking should you choose?
Pine (H3.2 treated) is the most popular and affordable option. It costs around $5 to $8 per linear metre and is available at Mitre 10, Bunnings and PlaceMakers nationwide. Good for standard residential decks. Needs oiling or staining to maintain appearance.
Kwila is a dense hardwood imported from the Pacific. It costs around $11 to $14 per linear metre but lasts 25 years or more with minimal maintenance. Naturally slip-resistant which makes it popular for pool decks and high-traffic areas. Requires pre-drilling to prevent splitting.
Macrocarpa is NZ-grown and naturally rot-resistant without chemical treatment. A sustainable local option with beautiful grain. Costs around $10 to $12 per linear metre. Good alternative to Kwila for those wanting a local timber.
Composite decking has the highest upfront cost at $18 to $25 per linear metre but requires almost no maintenance — no oiling, no staining, no rotting. Use an 8mm gap for thermal expansion. Popular for low-maintenance builds and rental properties.
How much does a deck cost per m2 in NZ?
Material costs only — pine deck around $80 to $120 per m2, Kwila around $120 to $180 per m2, composite around $200 to $350 per m2.
Add labour and you're looking at $250 to $600 per m2 fully installed depending on complexity, height off ground, and whether you need piles, bearers and joists included. A simple ground-level pine deck is at the low end. An elevated Kwila deck with steps and balustrades is at the high end.
Council consent is required for decks over 1.5 metres above ground in New Zealand.
Joist spacing guide for NZ decks
Most NZ residential decks use 400mm joist centres under pine decking. For Kwila and hardwoods you can use 450mm centres as the timber is denser. For composite decking check the manufacturer's spec — most require 400mm maximum.
Wider joist spacing saves on framing cost but can cause bounce underfoot. For decks over 30m2 or decks used for heavy gatherings, stick to 400mm centres.
Screws — what size and type for NZ decking?
Use 65mm screws for pine decking into H3.2 treated frames. Use 75mm screws for Kwila and hardwoods. Always use stainless steel or hot-dipped galvanised screws outdoors — standard zinc screws will corrode and stain your deck within a year in NZ conditions.
Budget for two screws per board per joist. A 100-screw box covers roughly 50 joist intersections. Our calculator estimates this automatically.
Related tools:
Paint Calculator NZ
Roofing Calculator NZ
Frequently asked questions
How do I calculate how much timber I need for decking?
Multiply deck length by width to get area in square metres. Divide by the board width in metres to get linear metres. For a 140mm board divide area by 0.14. Add 10% for waste. Our calculator does this automatically.
How much does a deck cost per m2 in NZ?
Materials alone run $80 to $200 per m2 depending on timber type. Fully installed with labour, piles, joists and bearers expect $250 to $600 per m2. Pine is cheapest, composite is most expensive but lowest maintenance.
How do I calculate decking?
Work out your deck area, divide by effective board width including gap, multiply by deck length to get linear metres, then divide by board length to get number of boards. Add 10% waste. Use our calculator to get boards and screws in one step.
How do you calculate decking per square metre?
A 140mm board with 5mm gap has an effective width of 145mm. Divide 1 by 0.145 to get 6.9 linear metres per square metre. For 90mm boards with 5mm gap you need 10.5 linear metres per square metre.