Deck board calculator
Estimate deck boards, stock lengths and a cut plan; a 3 m wide deck with 140 mm boards and 5 mm gaps takes 21 board rows.
- Runs in your browser
- No upload
- Instant result
Quantity estimate only. This does not approve structural safety, load capacity, drainage, fire resistance or building-code compliance. Verify the design and local requirements with a qualified professional. Purchase quantities round up to whole packs.
Assumptions & formula
Formula and assumptions
w = Waste allowance/100; n=ceil((W+gap)/(b+gap)); k=ceil(L/stock); N=ceil(nk(1+w))
Boards run along the platform length. Gaps are included across the width. Each board run rounds up to full stock lengths; offcuts are reported but not reused. Joists are counted across the width at the entered maximum spacing. No fastening or load-capacity approval.
The prefilled values are editable examples, not product specifications. Enter your supplier’s yield, density, coverage and packaging values, and add an allowance for overlaps, compaction and cuts where needed.
Purchase counts use the exact entered decimals and unit factors, without a rounding tolerance that could discard a real remainder. π and irrational square roots use enclosing bounds; ambiguous counts produce an error. Counts must be safe integers.
Results
Enter values and press Calculate to see the result here.
How to use this calculator
- Set inputs and units
Set the deck length and width, the finished board width and gap, and the usable stock length. Enter the joist spacing and a spare allowance.
- Calculate
Check this worked example: deck5×3 m,boardWidth0.1 m,gap0,stock3 m,spacing0.5 m,waste0% →runs30,stockPieces60,installed150 m,purchased180 m,offcuts30 m,joists11
- Results
Follow the actual cutting and width groups for each row. Spare boards are uncut extras outside the cutting plan.
Questions and limits
Are offcuts reused across rows?
No. Each row uses its own stock pieces. The last row may be ripped, or all rows narrowed equally when that is required.
Which input errors should I correct?
Gaps must leave a positive finished board width. Stock lengths and spacing must be positive, and you should use measured usable lengths.
What does this calculation leave out?
No offcut optimization, deduction for blade kerf or end trim, structural span approval, fixings or substructure design.