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)
- 12 ft
- Floor length (across joists)
- 20 ft
- Spacing (on centre)
- 16" OC
- Joist size
- 2×10
- Rows of blocking / noggins
- 1
- Joist hangers both ends
- Yes
- Include subfloor sheets
- Yes
- Subfloor sheet
- 4 × 8 ft
- Waste allowance
- 10%
the result is:
- Joists needed
- 16 joists
- Joists on layout
- 16
- Joist stock
- 12 ft
- Rim run
- 40 lin ft
- Blocking run
- 20 lin ft
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.
- Joist sizes and spans come from the Part 9 span tables in your provincial building code, the I-joist maker’s tables or your engineer.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the building code adopted in your province before ordering.