Decking Boards Calculator
How many deck boards a terrace needs, plus total linear metres and joist count.
Results
Boards needed
37
Area
15.00
m²
Length
100.0
m
Quantity
14
What this tool does
The gap between boards counts as part of each board's width, which is why a 145 mm board with a 5 mm gap covers 150 mm of deck. The joist estimate assumes supports every 400 mm, which suits most softwood decking.
Formula
boards = area ÷ (useful width × length) × (1 + waste)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
l | Length | m |
w | Width | m |
bw | Board width | mm |
bl | Board length | m |
gp | Joint width | mm |
wa | Waste allowance | % |
N | Boards needed | — |
A | Area | m² |
ML | Length | m |
J | Quantity | — |
Worked example
- Length5 m
- Width3 m
- Board width145 mm
- Board length3 m
- Joint width5 mm
- Waste allowance10 %
- Boards needed37
- Area15.00 m²
- Length100.0 m
- Quantity14
Limitations
- Always order a little more material than the calculated quantity. Cuts, breakage and pattern matching create waste that depends on the shape of the job.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.