Deck Board Calculator
Enter your deck size and board specs to get a row count, base quantity, and a waste-adjusted number of boards to buy.
Example deck shown — edit any value below
Not the nominal size — measure the board itself.
Recommended boards to purchase
58
- Deck area
- 240 sq ft
- Board rows
- 26
- Boards per row
- 2
- Base board quantity
- 52
- Waste allowance
- 10%
- Total stock board length
- 928 ft
- Estimated material cost
- $493.00
›Calculation details
This estimate assumes each board row is supplied independently. Efficient reuse of offcuts may reduce actual board quantity. Complex layouts may require additional material.
Actual quantity may change because of:
- Butt-joint placement
- Breaker boards
- Picture framing
- Diagonal layouts
- Unusable offcuts
- Manufacturer installation requirements
rows = ceil((144in + gap) / (board width + gap)) = 26
boards/row = ceil(runLength / stock length) = 2
base = rows × boards/row = 52
+waste → recommended = 58
How it works
The calculator first figures out how many rows of boards fit across your deck: each row takes up its actual width plus one gap, so N boards occupy N × board width + (N − 1) × gap — not a gap on every side of every board.
Next it figures out how many stock-length boards fit along a single row, multiplies rows × boards-per-row for a base quantity, then adds your waste percentage once and rounds up to a whole number of boards — the number you can actually buy.
Worked example
A 20×12 ft deck, boards running along the 20 ft length, 16 ft stock boards, 5.5 in actual board width, a 0.25 in gap, and 10% waste: 26 rows fit across the 12 ft width, each row needs 2 boards (240 in ÷ 192 in, rounded up), for a base of 52 boards. Adding 10% waste and rounding up gives 58 boards to buy — the same numbers the calculator above shows with its default example.
FAQ
Why isn't this the same as total linear footage ÷ board length?
Because leftover length from one row usually can't be reused in another row without extra cutting and joints. Counting boards per row separately gives a buildable, if slightly conservative, number.
What board width should I enter?
The actual measured width, not the nominal size printed on the label — a “5/4×6” board is not 6 inches wide. Measure the board itself.
Does this account for picture framing or diagonal layouts?
Not yet — this version assumes a straight layout. Picture framing, breaker boards, and diagonal patterns typically need more material than this estimate shows.