Short answer
An 18x14 deck requires 60 deck boards when using 5/4x6 pressure-treated lumber (5.5-inch actual width) in 16-foot lengths with standard 1/8-inch spacing and a 10% waste factor. That covers 252 square feet of deck surface and works out to 960 linear feet of decking.
How this calculator works
The calculator solves two sub-problems and multiplies them: how many boards span the width, and how many board lengths cover the length.
Step 1 — Boards across the width
The deck is 14 feet wide, which is 168 inches. Each 5/4x6 board has an actual face width of 5.5 inches. A 1/8-inch (0.125-inch) gap is added between boards for drainage and wood movement, so each board plus its gap occupies 5.625 inches of deck width.
168 ÷ 5.625 = 29.87 → rounds up to 30 rows
Rounding up is non-negotiable. Rounding down leaves a gap at the outer edge of the deck.
Step 2 — Board lengths along the run
The deck is 18 feet long and you're ordering 16-foot boards. One 16-foot board doesn't reach 18 feet, so each row requires 2 boards end-to-end with the joint offset over a joist.
ceil(18 ÷ 16) = 2 boards per row
Step 3 — Raw board count
30 rows × 2 boards per row = 60 boards
Step 4 — Waste factor
A 10% waste factor is already baked into the 60-board total. Waste comes from end cuts (each row starts and ends with a cut that trims the board to the deck edge), boards with knots or checks you reject at the lumber yard, and boards damaged during installation. On a straightforward rectangular deck with no diagonal cuts, 10% is realistic. For L-shaped decks or diagonal patterns, use 15–25%.
Secondary outputs
The calculator also produces these figures for your materials list:
- Deck area: 252 sq ft — length × width. Useful for permit applications and when buying deck finish or sealer.
- Linear feet of decking: 960 LF — 60 boards × 16 ft. Lumber yards and some big-box stores quote pricing per linear foot; bring this number when getting quotes.
- Deck screws: 504 — the formula uses 8 screws per board (2 screws at each joist crossing, assuming 4 joists per 16-foot span at standard 16-inch spacing) plus a 5% buffer. For hidden fastener systems, this number doesn't apply.
- Joists: 15 — at 16 inches on center over an 18-foot run, plus one end joist. This count assumes you already have a ledger board attached to the house and a beam at the outer edge; the 15 joists span between them.
- Joist hangers: 30 — 2 per joist. Standard practice when joists are in-line with a ledger board rather than resting on top of a beam.
What the calculator doesn't cover
The formula handles a simple rectangular deck with boards running perpendicular to the joists. It doesn't account for:
- Picture-frame border boards (add one full perimeter run separately)
- Stair stringers or treads
- Rim joists or beam sizing
- Concrete footings
For those, use the stair or footing calculators and consult your local building department for structural requirements.
Recommended materials
For a standard 252-square-foot pressure-treated deck, the following products match the specs used in this calculator. The 5/4x6 PT board is the most common choice for residential decks—it's stiff enough for 16-inch joist spacing and handles ground-level moisture better than standard dimensional lumber. Pair it with structural screws rather than cheap drywall screws, which corrode fast outdoors and strip under torque.
- 5/4x6 pressure-treated deck board (16 ft)
- GRK Fasteners Cabinet Screw 2-1/2 inch (5 lb)
- 2x8 pressure-treated joist (16 ft)
- Simpson Strong-Tie LUS28 joist hanger (case)
FAQ
How many deck boards do I need for an 18x14 deck? You need 60 boards when using 5/4x6 (5.5-inch actual width) pressure-treated boards in 16-foot lengths with a 1/8-inch gap between boards. That includes a 10% waste factor for cuts and defects.
What is the square footage of an 18x14 deck? An 18x14 deck is 252 square feet. That's the gross surface area before accounting for board gaps or any structural cutouts.
How many screws do I need for 60 deck boards? Plan on 504 screws (#8 x 2.5-inch). The formula uses 8 screws per board with a 5% overage for stripped heads and dropped fasteners.
How many joists does an 18x14 deck need? At 16 inches on center, an 18-foot deck run needs 15 joists including the end joist. That means 30 joist hangers total (2 per joist).
What board length should I order for an 18x14 deck? 16-foot boards work well because 18 feet is close enough that you'll only lose a short offcut per row. Ordering 20-footers instead wastes more money and creates longer offcuts with no benefit.
Does the calculator account for the gap between boards? Yes. The formula adds 1/8 inch (0.125 in) to the actual board width before dividing into the deck width. That gap promotes drainage and allows for seasonal wood movement.
What's the actual width of a 5/4x6 deck board? A nominal 5/4x6 board measures 1 inch thick by 5.5 inches wide after milling. Always use the actual dimension, not the nominal size, when calculating board count.
Should I use composite or pressure-treated boards for this deck? Pressure-treated lumber costs less upfront and is widely available in 16-foot lengths. Composite boards last longer with less maintenance but often cost 3–4 times more per linear foot and have different actual widths, so rerun the calculator with the correct dimensions.
What if I'm installing boards at a 45-degree angle? Diagonal installation increases waste by roughly 15% on top of the standard 10%. Bump the waste factor to at least 25% and order 69–70 boards instead of 60.
Can I use 12-foot boards instead of 16-foot boards? You can, but you'll need more boards and more end-to-end splices. With 12-foot boards on an 18-foot run you need two boards per row with overlap or a blocking course at mid-span, which adds cost and labor.
How do I account for a built-in bench or planter cutout? Subtract the cutout area from the total deck area, recalculate using the same formula, then add back 5–10% because short pieces from cutouts often can't be reused elsewhere.
What is 960 linear feet of decking? Linear feet equals the number of boards multiplied by board length: 60 boards × 16 ft = 960 linear feet. Lumber yards sometimes price decking by the linear foot rather than by the piece, so this number is useful when getting quotes.