How Do I Calculate Deck Boards?
Divide your deck width by board-width-plus-gap to get the row count, multiply by deck length for total linear feet, add a waste factor, then divide by your board length to get the number of boards to buy. A 16×12-foot deck using 5/4×6 boards (5.5 in actual) with a 1/8 inch gap, 16-foot boards, and 10% waste needs 26 rows, about 458 linear feet, and 29 boards.
Deck-board math is two steps. The first step counts how many parallel rows of decking fit across the width of the deck — a function of the deck width, the actual board width, and the gap you leave between boards for drainage. The second step multiplies that row count by the deck length to get total linear feet, adds waste, and converts to a count of pre-cut boards.
Row formula:Rows = ceil(deck width in inches ÷ (board width + gap)). Round up because partial rows still need a full board, and you'll rip the last one to fit.
Linear-feet formula:Linear ft = rows × deck length (ft) × (1 + waste %). Then divide by your chosen board length and round up for the count.
What Size Deck Boards Should I Use?
5/4×6 (5.5 in actual) is the standard residential pick — affordable, easy to walk on, and stocked everywhere. 2×6 (also 5.5 in actual) is structurally stronger and required for joist spacing wider than 16 in. Composite boards run 5.25 in wide. Narrow 5/4×4 (3.5 in actual) suits accent borders and small refined decks.
The width number on a deck board is nominal — the actual dimension is smaller. A 5/4×6 board is 5.5 inches wide because 1 inch is removed during milling and surface planing. This matters for layout: the calculator uses actual width, not nominal, because that's what your tape measure sees.
How Long Should Deck Boards Be?
Match board length to your deck's longest run if possible — a single 16-ft board across a 14-ft deck has fewer joints and looks cleaner than two 8-ft boards. Standard lengths are 8, 10, 12, 16, and 20 feet. Longer boards cost more per linear foot but reduce waste and improve appearance.
For decks longer than 20 ft, you'll need butt joints. Always land a butt joint on a joist (with the joist doubled or an H-clip for support), and stagger joints across rows so they don't line up — staggered joints distribute load and read as intentional rather than as a flaw.
What Gap Should I Leave Between Boards?
1/8 inch (0.125 in) is the standard gap for kiln-dried lumber, cedar, and composite. Wet pressure-treated boards install tight (no gap) because they'll shrink to roughly 1/8 in as they dry. The gap drains water, prevents debris from wedging boards apart, and lets the deck breathe through humidity cycles.
Some installers prefer a slightly wider 3/16 in gap (0.1875 in) for cedar in wet climates. Composite boards have manufacturer-specified minimums — check the spec sheet. Too small a gap holds water against the boards and accelerates rot; too wide and small debris falls through and looks sloppy.
How Much Waste Should I Plan?
10% for straight runs, 15% for diagonal layouts, 20% for decks with many cutouts. Waste covers cut offcuts, the occasional defective board, and trim cuts at the ends of each row. Diagonal patterns produce more angled offcuts; cutouts (around posts, planters, stair openings) generate extra offcuts at every penetration.
Composite vs. Pressure-Treated — Which Should I Use?
Pressure-treated wood costs less up front but needs staining or sealing every 1–2 years; composite costs 2–3x more but only needs annual cleaning. Total lifetime cost is similar over a 25-year horizon. Composite wins on maintenance time; pressure-treated wins on up-front budget and on color — nothing fades a composite board like ten years of sun.
- Pressure-treated softwood:$1.50–$3 per linear foot. 10–15 year service life with regular sealing. Easiest to cut and fasten.
- Cedar / redwood:$3–$5 per linear foot. Beautiful natural color, lighter than treated wood, but softer — dings easily under heavy furniture.
- Composite (capped polymer):$3–$7 per linear foot. 25+ year warranty, no sealing required. Heavier and more expensive, but lowest lifetime maintenance.
- Tropical hardwood (ipe, cumaru):$5–$10 per linear foot. 50+ year service life, dense enough to dull blades, requires pre-drilling. Premium choice for high-end decks.
Are Hidden Fasteners Worth It?
Required for grooved composite and most grooved hardwood boards; optional for softwood — and most pros face-screw softwood for speed and easy board replacement. Hidden fasteners cost roughly 3x more than coated face screws and slow installation by 30–50%. The clean look matters most on composite where face-screw heads stand out against the smooth surface.
How Many Deck Boards for Common Deck Sizes?
Pre-calculated counts using 5/4×6 (5.5 in actual) boards with a 1/8 inch gap and 10% waste, assuming the longest available board length matches the deck length:
- 10×10 deck (100 sq ft) — 22 rows, ~242 linear ft, ~16 boards (10 ft)
- 12×12 deck (144 sq ft) — 26 rows, ~343 linear ft, ~22 boards (16 ft)
- 12×16 deck (192 sq ft) — 26 rows, ~458 linear ft, ~29 boards (16 ft)
- 14×16 deck (224 sq ft) — 31 rows, ~546 linear ft, ~35 boards (16 ft)
- 16×20 deck (320 sq ft) — 35 rows, ~770 linear ft, ~39 boards (20 ft)
Cost varies by region. The Estimated Material Cost card pulls from our indicative national-average pricing dataset(refreshed quarterly). Northeast and California metros run 15–40% above the national midpoint while Midwest and Southeast metros run 5–15% below — verify locally for binding quotes.
How Much Does 5/4×6 PT Pine Decking Cost?
5/4x6 PT pine decking averages about $1.85 per linear foot nationally as of our April 2026 research. 5/4 × 6 PT pine. Regional variation is significant — Northeast and California metros run 15–40% above the national midpoint while Midwest and Southeast metros run 5–15% below. See our pricing methodology for sources and confidence tiers.
Related Calculators
- Concrete Calculator — Footing pours for deck posts
- Fence Post Calculator — Post counts and concrete bags for the deck's perimeter
- Gravel Calculator — Drainage gravel under freestanding decks
Written by Daniel McCarney — AceCalc