Decking Calculator
Estimate the decking boards, joists and screws for a rectangular deck. Change the board size, gap and joist centres to match the timber you plan to buy.
- Deck area
- 14.40 m²
- Decking boards
- 24 × 4.8 m (100.8 lineal m before waste)
- Joists
- 12 × 3.0 m (36.0 lineal m)
- Deck screws
- about 504
Need someone to do the job? Find fencing & decking or builders near you and contact them directly, with no lead fees.
How it works
- Rows of boards = deck width ÷ (board width + gap), rounded up. Lineal metres of board = rows × deck length.
- Boards to buy = lineal metres plus the waste allowance, divided by your board length, rounded up.
- Joists run across the boards at the centres you enter, plus one at the end. Screws assume two per board at every joist.
These are estimates for planning and comparing quotes, not a substitute for a professional's measurements.
Common questions
What joist spacing should I use?
It depends on the board thickness and the timber. 450 mm centres are common for 32 mm decking boards, and thinner boards need closer joists. Follow the supplier's span tables or NZS 3604.
How big a gap should I leave between deck boards?
Usually 3 to 6 mm, so water drains and the timber can move. Use the gap the board supplier recommends.
Do I need a building consent for a deck?
Often not, if no part of the deck is more than 1.5 metres above the ground. Any deck with a fall of 1 metre or more needs a safety barrier. Check with your council if you are unsure.