This calculator tells you how many deck boards you need to surface a rectangular deck, and how many total linear feet that comes to. Enter the deck’s length and width, the actual width of your boards, and the gap you will leave between them.
It works for pressure-treated lumber, cedar, and composite decking. Boards are assumed to run along the deck’s length, in a single run with no seams — the most common layout for decks up to 20 ft. If your boards will run the other way, just swap the length and width you enter.
Worked example: a 16 × 12 ft deck with 2×6 boards
Take a deck 16 ft long and 12 ft wide, surfaced with standard 2×6 boards. A “2×6” board is actually 5.5 inches wide, and you plan a 1/4 inch gap between boards.
- Row pitch: each board plus its gap takes up 5.5 + 0.25 = 5.75 inches across the deck’s width.
- Board count: the width is 12 ft = 144 inches, so 144 ÷ 5.75 = 25.04, rounded up to 26 boards.
- Linear feet: each board spans the 16 ft length, so 26 × 16 = 416 linear feet of decking.
- Buying: the deck divides neatly into 16 ft boards — 26 of them, with no end seams. It is still worth adding two or three spares for boards that warp, split, or get miscut (see below).
How the calculation works
Boards = deck width (inches) ÷ (board width + gap), rounded up, and linear feet = boards × board length.
Two details matter more than the arithmetic. First, use the actual board width, not the nominal name: a 2×6 is 5.5 inches wide and a 2×4 is 3.5 inches, per standard US lumber dimensions. Second, the gap is a real part of the layout, not a rounding error — across 26 boards, quarter-inch gaps add up to more than six inches of width. Recommended gaps depend on the material: many composite manufacturers specify about 1/4 inch side-to-side, while dry pressure-treated lumber is often installed nearly tight because it shrinks as it dries. Always follow the gap figure in your board maker’s installation guide. More on our sources and testing is on the How We Calculate page.
Typical decking costs
Decking boards only — framing, footings, fasteners, and railing are separate. Typical US prices, checked November 2026:
| Material (16 ft board) | Typical price |
|---|---|
| Pressure-treated lumber, 2×6 | $18–$28 per board |
| Cedar, 2×6 | $35–$65 per board |
| Wood-plastic composite | $25–$85 per board |
| Hidden fastener clips (composite) | $0.50–$1.00 each |
For the example deck, 26 pressure-treated boards at about $23 each come to roughly $600 of decking; the same deck in mid-range composite is roughly $1,400.
Before you buy
- Decide the board direction first. Boards usually run perpendicular to the house or along the deck’s longest dimension — the direction changes the count, so enter dimensions to match your layout.
- Confirm the actual width and available lengths of the specific product. Choosing 16 ft boards for a 16 ft run (as in the example) removes every seam; a 12 ft deck might be cheaper to cover with 12 ft boards even if the per-foot price is higher.
- Use the gap your manufacturer specifies, especially for composite — warranty coverage often depends on it.
- Order a few spare boards beyond the calculator’s count. The tool counts a perfect layout; real decks lose boards to warping, end splits, and cutting mistakes, and spares from the same batch match best.
- For a diagonal or picture-frame layout, expect roughly 10–15% more boards than the straight count, and set expectations accordingly before ordering.
- Check what your deck frame needs while you are at it — if you are pouring small concrete pads or footings, our Concrete Calculator covers the volumes. (Sizing footings is a code question for your local building department, not something any calculator here decides.)
Frequently asked questions
How many boards do I need for a 12 × 16 ft deck?
With 5.5-inch boards and a 1/4 inch gap, 26 boards — the worked example above is exactly that deck. If the boards run the short way instead (spanning 12 ft across a 16 ft width), the count becomes 34 shorter boards; total linear feet is nearly the same.
What gap should I leave between deck boards?
For most composite products, about 1/4 inch side-to-side, per the manufacturer’s guide. For pressure-treated lumber, boards are often installed with little or no gap while still wet, because they shrink as they dry and open the gap themselves. Your board maker’s instructions override any general rule.
Does this include joists, beams, or footings?
No. This calculator covers the decking surface only. Framing lumber, concrete, and hardware are separate materials, and framing spans are set by code tables and your local building department — not by a material estimator.
Why does the board count seem high compared to simple area math?
Because the gap counts. Dividing the deck area by board area alone ignores the space between boards; the pitch method used here includes the gap in every row, which is how the deck will actually be covered.
How do I calculate for a deck that is not a rectangle?
Break it into rectangles, run the calculator for each, and add the board counts. Our Square Footage Calculator can help you work out the areas of each section first.
Related calculators
Building the base under a ground-level deck or a gravel pad instead? Our Gravel Calculator works out the stone for the pad. And if the project grows into a full patio, the Concrete Calculator handles the slab.
Estimates only: actual board counts vary with layout, product dimensions, and on-site cuts. Confirm measurements and manufacturer specifications before buying. This calculator estimates material quantities for common DIY projects; it does not cover structural or load-bearing design, including deck framing and footings, or electrical, gas, or plumbing work.