About this calculator
Count the parts of a deck frame: joists, rim and ledger, beams, 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 × 900 mm round.
Worked example
With these inputs:
- Deck length (along house)
- 4.8 m
- Deck depth (out from house)
- 3.6 m
- Joist spacing
- 400 mm
- Attached to house (ledger)
- Yes
- Beam lines
- 1
- Post spacing along beam
- 1.8 m
- Post height
- 600 mm
- Joist size
- 47 × 150
the result is:
- Joists
- 13 joists @ 400 mm
- Deck area
- 17.28 m²
- Joist stock
- 3.6 m
- Footings (300 × 900 mm)
- 0.25 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 UC4 ground-contact treated timber for posts and anything close to the ground.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the Building Regulations before ordering.