Face width plus gap is the module
Measure the dimension perpendicular to the boards as deck width. Each row is actual face width plus the gap you will leave — a 5.5 in board with a 1/8 in gap is not a 6 in module. Stock length is the board you can buy, usually the long run of the deck.
Picture-frame borders, breaker boards and bad ends eat waste. Keep the percentage visible so a later estimator can change it.
Joists are not boards
Joist count, beam size and post layout sit with the framing professional. This page only counts decking. Stain gallons are a companion fence/deck stain takeoff, not a hidden coat inside the board count.
Do it in order
- Enter board-run length, deck width, actual face width and the gap you will leave.
- Type the stock length you can buy, not a theoretical infinite plank.
- Apply cut waste, then keep joists, railing and stain on other lines.
Worked example — 16 ft run × 12 ft width, 5.5 in board, 1/8 in gap, 10% waste
Each row is 5.625 in on center, so 12 ft needs 26 rows. At a 16 ft stock length that is 416 ft of net boards before waste. With 10% waste the order is 29 boards. A picture-frame border is extra miters — raise waste.
Planning boundary
This is a board count. It does not design a deck structure, a guardrail or a live lumber price.
Does this size the joists?
No. Span, species and fastener schedule stay with the responsible professional.
What if stock is 12 ft not 16 ft?
Change the stock-length input. A shorter plank means more end joints, not a scaled 29.
Is composite the same math?
The count is the same if face and gap match. Hidden clips and grooved edges can change waste — enter that honestly.