Board rows, stock lengths, and offcuts
The estimate allocates enough full stock boards to each row, then adds your spare-board percentage. Purchased length above the row runs includes offcuts and spare boards; it does not include waste from ripping the final row narrower.
If your lumber quote is priced by volume, the Board Foot Calculator converts board dimensions into board feet.
The formula
There is one fewer gap than boards in a run of adjacent rows. Adding a gap to the numerator accounts for that boundary. Each row receives its own rounded stock allocation; scraps are not reused across rows. Both parallel directions are evaluated by swapping the board run and the dimension across rows. The comparison chooses fewer whole order boards, with the entered run winning a tie. Board material cost is order boards times the entered price.
Worked example
A 4 m run across a 3 m deck uses 21 rows of 140 mm boards with 5 mm gaps. Each row needs one 4.8 m stock board. Adding 10% and rounding up gives 24 boards, or 115.2 linear metres purchased.
How to use this calculator
- Choose metric or feet/inches and enter the deck dimensions. Unit switches convert existing entries.
- Enter the actual board width, product-specified side gap and available stock length.
- Choose a direction or compare both, then enter spare-board allowance and a board price.
An order estimate for a defined layout
The last row may need ripping to fit the remaining width. A picture-frame border, diagonal boards, stairs, or decorative inlays require a separate plan. Because offcuts are not reused, this model can overestimate material when a good cutting plan permits several short rows to share one stock board.
Gaps and structural support
Side gaps depend on the decking product and installation conditions. Follow its installation guide rather than treating the example gap as a universal specification. When a run exceeds stock length, joints need appropriate support and may require additional trimming. This tool counts surface boards only; joists, beams, footings, fixings, and structural compliance are outside its scope.
Comparing the two board directions
The direction table rounds stock boards per row before applying your extra-board allowance. A shorter board run can still need more stock if the other deck dimension needs many more rows. The comparison minimizes order boards, with no cross-row reuse of offcuts.
Assumptions & limitations
What this calculation assumes
- Every row runs in the same direction; each row has a separate stock allocation.
What to keep in mind
- No end-joint gaps, saw kerf, structural design, or offcut optimization.
Common questions
Does the allowance include the last narrow row?
The row count already includes that row. The extra allowance adds whole boards on top of the base allocation.
Why can long boards make this estimate conservative?
The model does not cut one stock board into pieces for several rows. Review reusable offcuts in a project-specific cut list.
Sources & further reading
Reviewed on