Deck Board Calculator
This deck board calculator counts the decking for any rectangular deck from its length and width, in feet or meters. Pick your board width, gap and stocked length, and it returns rows of decking, linear footage with a separate 10% waste line, whole boards to buy — and the joists underneath.
Metric options use regional material sizes. Check your selected sizes after switching units.
Deck boards (16 ft)
29boards
- Rows of decking26 rows
- Linear feet before waste416 linear ft
- With 10% waste457.6 linear ft
- Joists needed13 joists
Updated .
How the deck board count is calculated
Decking is counted in rows across the deck’s width, then converted to linear footage and whole boards:
linear ft = rows × deck length
buy = ceil(linear ft × (1 + waste ÷ 100) ÷ board length)
joists = ceil(deck length ÷ joist spacing) + 1
There are gaps between boards, but no extra gap after the final row. Adding one gap to the deck width before dividing accounts for that edge. The repeating width is one board plus one gap — 5.5″ + 0.25″ = 5.75″ for standard 5/4×6 decking — and the division rounds up because a deck that needs 25.09 rows gets 26, with the last board ripped to fit. Rows times deck length gives the raw linear footage.
The 1.10 factor is your 10% waste, shown as its own line in the results: it covers cutting 16-foot stock down to a 16-foot deck (you lose trim on every board), the boards you reject for cupping, and butt-joint offcuts. Dividing the with-waste footage by your chosen board length and rounding up gives whole boards at the register.
Note on butt joints: because the board count divides pooled linear footage by stock length, it assumes offcuts get reused — rows longer than one board are pieced together with butt joints landing over a joist, and the cut-off end of one board starts another row. If you want every row to be a single unbroken board with no butt joints, order one board per row instead (rounded up to the next stocked length that covers your deck length) — that usually means more boards than the pooled count shown here.
Joists run across the deck length at your spacing — 16″ on center by default — and the +1 closes the far end, same as the last stud in a wall.
Worked example: a 16 × 12 ft backyard deck
Say you’re decking a 16-foot by 12-foot platform off the back door with 5/4×6 boards (5.5″ wide), a 1/4″ gap, and 16-foot stock so every board runs full length. Those are the defaults loaded above.
- Rows: the deck is 12 ft = 144″ wide. (144 + 0.25) ÷ 5.75 = 25.09, rounded up to 26 rows — the last row gets ripped narrow.
- Linear footage: 26 rows × 16 ft = 416 linear ft of decking before waste.
- Waste: 416 × 1.10 = 457.6 linear ft once trim cuts and culled boards are covered.
- Boards: 457.6 ÷ 16 = 28.6, rounded up to 29 boards.
- Joists: 16 ft = 192″ of deck length at 16″ on center: 192 ÷ 16 = 12, + 1 = 13 joists.
So the decking order is 29 sixteen-footers over 13 joists. If your supplier only stocks 12-foot boards, switch the length select: same 457.6 linear feet becomes 39 boards, and every row picks up a butt joint — which is exactly why full-length stock is worth chasing.
How many deck boards do I need for a 12×16 or 16×20 deck?
The table below covers popular deck footprints using the defaults: 5.5″ boards, a 1/4″ gap, 16-foot stock, and the 10% waste factor already baked into the board count. Boards run parallel to the first dimension.
| Deck (L × W) | Sq ft | 16 ft boards | Joists @ 16″ OC |
|---|---|---|---|
| 10 × 10 ft | 100 | 15 | 9 |
| 12 × 10 ft | 120 | 18 | 10 |
| 12 × 12 ft | 144 | 22 | 10 |
| 14 × 12 ft | 168 | 26 | 12 |
| 16 × 12 ft | 192 | 29 | 13 |
| 16 × 16 ft | 256 | 38 | 13 |
| 16 × 20 ft | 320 | 47 | 13 |
| 20 × 16 ft | 320 | 47 | 16 |
Look at the last two rows: a 16 × 20 and a 20 × 16 deck are the same 320 square feet and the same 47 boards, but running the boards the long way costs three extra joists. Board direction is a framing decision as much as a looks decision.
Frequently asked questions
What gap should I leave between deck boards?
A 1/4″ gap is the safe default for drainage and debris clearance, and it’s what this calculator assumes. The exception is wet pressure-treated lumber: it arrives swollen and shrinks as it dries, so many builders lay it nearly tight and let the gap open up to roughly 1/4″ on its own. Composite also moves with temperature; use the product’s side-gap and end-gap instructions for the installation conditions.
How much extra should I add for diagonal decking?
Bump the waste from 10% to about 15%. Every board on a diagonal deck ends in a 45-degree cut, and the offcut from one end rarely fits the other, so scrap piles up faster than with square-laid boards. Set the waste allowance under more options. The tool still assumes straight rows; a diagonal layout needs a separate cutting plan and may need different joist spacing. Diagonal looks sharp — just budget for it.
Are composite deck boards the same width as wood?
Mostly yes — mainstream composite lines are milled to the same 5.5″ face as a 5/4×6 wood board, so the default here works for both. The differences are elsewhere: composite is sold almost exclusively in 12, 16, and 20-foot lengths, grooved-edge boards for hidden fasteners can’t be ripped without exposing the groove, and solid-edge boards for the perimeter cost more. Check the width on the spec sheet before ordering, not at delivery.
How many screws do I need for my decking?
Figure about 3.5 screws per square foot with boards on 16″ centers — two screws at every board-joist crossing. For the 16 × 12 ft worked example, that’s 192 sq ft × 3.5 ≈ 672 screws, so buy a 5-lb box rather than counting. Use coated or stainless screws rated for your material; ordinary deck screws react badly with the copper in modern pressure-treated lumber, and hidden-fastener composite systems come with their own clip counts.
Should deck boards run parallel to the house or away from it?
Structurally, boards must run perpendicular to the joists — so decide the look you want first, then frame for it. Boards laid parallel to the house (the common choice) mean joists running away from the wall, hung off a ledger. As the table above shows, orientation changes the joist count for the same square footage, so run your actual layout through the calculator both ways before ordering framing lumber.
Sources and assumptions
- American Wood Council: Understanding Loads and Span Tables — Member sizes and permitted spans depend on loads, species, grade, and support conditions. This calculator estimates geometry and quantities.
These results are planning estimates only — verify quantities with your supplier and local building code before you buy or build. See our terms of use.