About this calculator
Count the parts of a deck frame: joists, rim and ledger, bearers, posts, footings and the connectors that tie it all together.
How it’s calculated
Joists = (deck length ÷ spacing) + 1. Each beam line is two plies the full deck length. Posts = (deck length ÷ post spacing) + 1 per beam line, plus a front line if the deck is freestanding. Footings default to 300 mm × 600 mm round.
Worked example
With these inputs:
- Deck length (along house)
- 4.8 m
- Deck depth (out from house)
- 3.6 m
- Joist spacing
- 450 mm
- Attached to house (ledger)
- Yes
- Bearer lines
- 1
- Post spacing along bearer
- 1.8 m
- Post height
- 600 mm
- Joist size
- 140 × 45 H3 pine
the result is:
- Joists
- 12 joists @ 450 mm
- Deck area
- 17.28 m²
- Joist stock
- 3.6 m
- Footings (300 × 600 mm)
- 0.17 m³
Tips from the trade
- A ledger needs flashing and proper structural fasteners into the house rim. Nails alone are not enough.
- Joist tape on the tops of the joists greatly extends frame life under composite boards.
- Use H4 treated pine or a durable hardwood for posts in the ground, and at least H3 for the frame above ground. Seal every cut end.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the NCC and Australian Standards before ordering.