How the calculation works
- Rows of boards = deck width in inches ÷ (actual board width + gap), rounded up.
- Boards per row = deck length ÷ board length, rounded up.
- Boards = rows × boards per row, plus any extra percentage you add.
- The default gap is 3/16 in between boards, as Trex recommends for its composite decking.
Example
Deck length (along the boards): 16 ft · Deck width (across the boards): 12 ft · Actual board width: 5.5 in · Board length: 16 ft · Gap between boards: 0.1875 in · Extra boards: 0 %
Result: 26 boards.
Tips before you buy
- Use the actual board width from the product page — a nominal 6 in board is often 5.5 in wide.
- Pick a board length that divides your deck length evenly to cut less waste.
- Follow your board manufacturer's gap and fastening instructions.
- Always confirm coverage and yield with the manufacturer's label — products differ.
- Surface boards only — not the deck frame or its supports.
FAQ
Does this include the deck frame?
No. It counts surface boards only. The frame underneath is structural and outside the scope of this calculator.