Deck Board Calculator

How this calculator works

This calculator estimates deck board rows and board counts from deck size, board width, gap, board length, direction, and waste. It supports metric and imperial inputs and reports total linear length in both metres and feet.

Use it for early lumber/timber ordering estimates. Borders, breaker boards, stairs, angled layouts, board staggering, and exact seam placement can change the final count.

Formula

• If boards run along deck length: board rows = ceiling(deck_width / (board_width + gap)); linear length needed = board rows x deck_length.
• If boards run along deck width: board rows = ceiling(deck_length / (board_width + gap)); linear length needed = board rows x deck_width.
• Boards before waste = ceiling(linear length needed / board length).
• Boards after waste = ceiling(boards before waste x (1 + waste_percent / 100)).
• Estimated cost = boards after waste x board price.

Worked example

For a 4.8 m by 3.6 m deck using 140 mm boards with 5 mm gaps, with boards running along the deck length, board coverage is 145 mm.

Board rows are ceiling(3.6 / 0.145) = 25. Linear length is 25 x 4.8 = 120 m. If each board is 4.8 m, that is 25 boards before waste.

Common mistakes

• Using nominal board width instead of actual board width.
• Forgetting the planned gap between boards.
• Ignoring borders, breaker boards, stairs, diagonal layouts, and seam patterns.
• Treating the estimate as a final cut plan instead of checking the real deck layout.

FAQs