How Many Deck Boards Do I Need?

A 12×16 ft deck with 5½" boards and a ⅛" gap needs about 26 rows. With 16-foot stock and 10% waste, buy roughly 29 boards.

The short count shows up mid-morning. You divide square footage by board face, forget the gap, and load two dozen sticks. The last row still needs a rip and another full board. The crew waits while someone makes a second lumber run.

The deck-board formula is:

rows = ceil(deck width in inches ÷ (board width + gap))

Then multiply rows by how many stock lengths fit each row, and add about 10% waste for splits, crowns, and the final rip. Use the actual face width, not the nominal 1×6 stamp. Estimate only — not engineering or building-code advice.

How many deck boards for a 12×16 deck?

Run the boards the 16 ft direction so each row is one 16-foot stick. Count rows across the 12 ft width.

Width = 12 × 12 = 144 in. Pitch = 5.5 + 0.125 = 5.625 in. 144 ÷ 5.625 ≈ 25.6 → round up to 26 rows. That is 26 boards before waste. Add 10% → 26 × 1.10 ≈ 28.6 → buy 29.

Shorter stock changes the order. The same 16 ft run with 12-foot boards needs two sticks per row → 52 net before waste. Match stock length to the joist span you framed so you are not splicing mid-bay for looks you did not plan.

The formula, on a tape

Measure the deck width perpendicular to the board direction. Measure actual board face from the stack you will buy — kiln-dried PT, cedar, and composite faces differ.

• Width (in) = feet × 12
• Pitch = actual board width + gap between faces
• Rows = ceil(width ÷ pitch)
• Boards per row = ceil(deck length ÷ stock length)
• Order ≈ rows × boards per row × 1.10 (waste)

Example: 10×14 deck, 5.5 in boards, ⅛ in gap, 14 ft stock. Width = 120 in. Pitch = 5.625 in. 120 ÷ 5.625 ≈ 21.33 → 22 rows. One stick per row → 22 net. With 10% waste, order about 25.

In Deck Takeoff Master you enter size, board face, gap, and stock once. It returns boards, joists, and a material list on your phone. Free for a simple takeoff; Pro unlocks extras at $9.99.

Three mistakes that short the board order

Forgetting the gap. Divide width by 5.5 alone and you invent an extra row that does not exist — or worse, ignore gap and under-order when the layout needs space for drainage. Gap is the clear space between faces, usually about ⅛ in for wet PT (it shrinks) and the product gap for composite. Pitch is width + gap. Skip it and the last bay does not close clean.

Ordering exact net count. The net count assumes every board is straight, dry, and cut clean. Splits at the screw, crowns that will not sit, and the final edge rip eat 5–15%. Ordering exactly 26 for a 12×16 leaves you one short board from a second trip while joists are already waiting. Buy the allowance. Leftover decking is cheaper than a stalled crew.

Using nominal width. A “1×6” is not 6 in wide. Dressed lumber is closer to 5.5 in; some composites sit near 5.25 in. Divide by 6 and you under-order by roughly one board every twelve feet. Always measure a sample from the bundle or carton you will buy.

Diagonal layouts and picture frames

Straight boards perpendicular to joists are the chart above. A 45° diagonal layout typically needs about 15–20% more material than straight — plan closer to 15% waste on top of the net, or run the app with a higher waste factor. Herringbone and chevron patterns burn still more; treat those as a separate takeoff, not a quick chart.

Picture-frame borders (a perimeter rim around the field boards) add linear feet that are not in the row count. Order the field from the formula, then add border pieces by perimeter. Joists still set the structure — typical residential spacing is 16 in on centre; confirm span tables and local code before you buy lumber for the frame.

Worked example with a rip

Deck: 12×16 ft, 5.5 in boards, ⅛ in gap, 16 ft stock, straight layout.

Rows: 144 ÷ 5.625 ≈ 25.6 → 26 rows. Net boards: 26. Waste at 10% → order 29. The last row may need a rip to land flush at the rim — that rip comes from one of the waste boards, not from inventing a 27th full stick in the net count.

Joists for that same deck sit next door on the EBN Build Calculators hub. For boards, joists, and a printable material list, open Deck Takeoff Master. Stairs off the deck use Stair Stringer Master — or read the Stair Stringer Master review.

These counts are estimates only — not engineering or building-code advice. Product span, fastener schedules, and local code can change board size and gap. Measure the actual face. Add the gap. Order the waste.

Estimate only — not engineering or building-code advice.