About this calculator
Count floor joists, rim joists, hangers and blocking for a floor or deck frame, plus subfloor sheets. Joist size and span must come from span tables or your engineer. This tool counts materials; it does not size the joists.
How it’s calculated
Joists = ceil(floor length ÷ spacing) + 1. The rim is two runs of the floor length. Each blocking row has one piece per bay.
Worked example
With these inputs:
- Joist length (span)
- 3.6 m
- Floor length (across joists)
- 5 m
- Spacing (on centre)
- 400 mm centres
- Joist size
- 47 × 195 C24
- Rows of blocking / noggins
- 1
- Joist hangers both ends
- Yes
- Include subfloor sheets
- Yes
- Subfloor sheet
- 2440 × 1220 mm
- Waste allowance
- 10%
the result is:
- Joists needed
- 14 joists
- Joists on layout
- 14
- Joist stock
- 3.6 m
- Rim run
- 10 lin m
- Blocking run
- 5.2 lin m
Tips from the trade
- Double the joists under parallel walls and around stair openings.
- Glue and screw subfloors to reduce squeaks.
- Crown every joist the same way, usually crown up.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the Building Regulations before ordering.