How to use
- Enter deck dimensions and board dimensions.
- Choose the direction boards run.
- Review board rows, pieces per row, and total boards to buy.
Input guide
- Board width and gap are entered in inches.
- Board length is the stock board length in feet.
- Price per board is optional and not live pricing.
Common mistakes
- Ignoring the gap between boards.
- Mixing up board run direction and deck width.
- Using this for joists, beams, footings, stairs, or railings.
Assumptions and limitations
- No joist span, beams, footings, stairs, railing, structural design, or code advice is included.
- The deck surface is treated as a simple rectangle.
- Waste is a percentage allowance, not an optimized cut plan.
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Formula
- Board module = board width + gap, converted to feet.
- Board rows = deck width across boards / board module, rounded up.
- Pieces per row = board run length / board length, rounded up.
- Boards to buy = rows x pieces per row x waste factor, rounded up.
Example
A 12 ft x 16 ft deck with 5.5 in boards, 0.125 in gaps, and 12 ft boards needs 35 rows and 2 pieces per row, or 77 boards with 10% waste.
FAQ
Does this calculate framing lumber?
No. It only estimates surface decking boards for a simple rectangular deck.
Should I include board gaps?
Yes. The gap changes how many rows fit across the deck width.