How many deck boards do I need?
This page counts board rows across the deck width. A 13 ft by 6 ft deck is 78 sq ft. With 5.5 inch boards and 0.25 inch gaps, the calculator estimates 13 rows before waste and 15 boards with 10% waste.
Board rows vs board lengths
The board count tells you how many rows of decking cross the deck width. Stock board lengths, butt joints, seams, picture-frame borders, breaker boards, and diagonal layouts must be planned separately before purchasing.
What is not included
This calculator estimates the main deck surface boards only. Joists, beams, posts, footings, railing, stairs, fascia, fasteners, clips, blocking, and trim are separate material lines.
When to split the deck estimate
Split the deck into sections when board direction changes, when part of the deck uses a different board width, or when a pool edge, porch cutout, stair landing, or picture-frame border adds extra cuts.
Deck board example counts
Examples use 5.5 in boards, 0.25 in gaps, and 10% waste. Board length, seams, fascia, stairs, railings, and framing are separate.
| Deck size | Board rows before waste | Boards with 10% waste |
|---|---|---|
| 12 ft x 12 ft deck | 26 rows | 29 boards |
| 12 ft x 16 ft deck | 34 rows | 38 boards |
| 12 ft x 20 ft deck | 42 rows | 47 boards |
| 16 ft x 20 ft deck | 42 rows | 47 boards |
| 20 ft x 20 ft deck | 42 rows | 47 boards |
Before you calculate
- Measure deck length in the direction boards run.
- Measure deck width across the board rows because width drives the row count.
- Use actual installed board width and planned board gap, not just nominal product size.
Common mistakes
- Treating board-row count as a full deck material list.
- Forgetting stock board lengths, seams, picture-frame borders, stairs, and fascia.
- Using nominal board width when actual width is different.
Formula
boards = ceil((deckWidth * 12 / (boardWidth + gap)) * (1 + wastePercent / 100))
Assumptions
- Deck quantities depend on board width, spacing, layout direction, stairs, railing, cuts, and waste.
- Estimate boards, framing, railing, fasteners, trim, coating, and disposal separately when needed.
- Structural spans, permits, guardrail requirements, and code approval are separate.
Example
Estimated deck boards needed: 14 boards
How to estimate deck board count
- Enter deck length and deck width in feet so the calculator can estimate the deck surface and board rows.
- Convert deck width to inches, then compare it with the board width plus the planned board gap.
- Divide deck width by board width plus gap to estimate board rows, then round up to whole boards.
- Add waste for cuts, damaged boards, board selection, layout changes, and starter or end-board trimming.
- Check stock board lengths, seams, picture-frame borders, stairs, fascia, fasteners, railing, and framing separately before ordering.
Before you buy materials
- Round up to full boards and plan board lengths before purchasing.
- Estimate joists, beams, posts, footings, railings, fasteners, and finish materials separately.
FAQ
How do I calculate decking boards needed?
Divide deck width in inches by board width plus gap, round up to whole rows, then add waste. Plan board lengths and seams separately.
How many boards for a 12 x 16 deck?
With 5.5 inch boards, 0.25 inch gaps, and 10% waste, a 12 x 16 deck needs about 37 board rows when boards run along the 12 ft length.
Does this include joists and framing?
No. It estimates decking surface boards only. Framing, posts, railings, stairs, fasteners, and footings should be estimated separately.
Does board gap affect the count?
Yes. A larger gap increases the spacing between board rows, which can reduce row count slightly. Use the gap recommended for the product and installation conditions.
Should I add waste for decking?
Yes. Waste covers cuts, defects, board selection, end trimming, and layout changes. More complex layouts may need a higher waste percentage.
Related calculators
This calculator is for planning estimates only. Verify final quantities with product labels, project conditions, and a qualified professional when accuracy matters.