Deck Calculator
Work out the deck boards and joists for a rectangular deck from its size, board size, gap and joist spacing.
Deck boards (16 ft)
29
- Board rows
- 26
- Linear feet of decking
- 416 ft
- Joists
- 13 × 12 ft
- Deck area
- 192 ft²
Joist sizes and spans depend on load and species — follow your local code. Material counts are estimates — check with your supplier and local code before you buy.
Show the work
Board rows across the deck, rounded up
rows = ⌈width × 12 ÷ (board width + gap)⌉
⌈12 × 12 ÷ (5.5 + 0.125)⌉ = 26
Boards per row, rounded up
per row = ⌈length ÷ board length⌉
⌈16 ÷ 16⌉ = 1
Boards, plus waste, rounded up
boards = ⌈rows × per row × (1 + waste ÷ 100)⌉
⌈26 × 1 × (1 + 10 ÷ 100)⌉ = 29
How it works
Rows = ⌈deck width ÷ (board width + gap)⌉; boards = rows × ⌈deck length ÷ board length⌉ × (1 + waste); joists = ⌈deck length ÷ spacing⌉ + 1
Questions
- How does the deck calculator work?
- Rows = ⌈deck width ÷ (board width + gap)⌉; boards = rows × ⌈deck length ÷ board length⌉ × (1 + waste); joists = ⌈deck length ÷ spacing⌉ + 1.
- What do I need to enter?
- Deck length (along the boards), Deck width (across the boards), Board width (actual), Gap between boards, Board length, Joist spacing, Extra for waste. Optional fields can be left blank.
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