Deck Board Spacing Guide

Decking is sold by the linear foot or in standard board lengths — commonly 8, 12, or 16 feet. Your order quantity comes from deck area divided by effective board coverage per row, and that coverage includes the gap between boards. A 5.5-inch board with a quarter-inch gap covers about 5.75 inches per row. Ignore the gap and you under-order by roughly 4 percent — enough to come up short on a large deck.

Spacing also affects drainage and drying. Tight gaps trap moisture between boards, which accelerates rot on natural wood and can void composite manufacturer warranties. Wider gaps improve airflow but may feel less comfortable for bare feet and can allow small debris to collect.

Hidden fastener systems often require a specific gap — usually 1/8 inch — because the clip determines the spacing. Face-screwed boards give you more flexibility, but you still need a consistent gap for a professional appearance and predictable material math.

Pressure-treated southern yellow pine: 1/8 to 1/4 inch gap when installed dry. If boards are wet at install, use a thinner gap — they shrink as they dry. Many installers use a 16d nail (about 1/8 inch) as a temporary spacer.

Cedar and redwood: 1/4 inch is common for kiln-dried boards. These species move more with humidity changes than composite, so consistent spacing prevents binding.

Composite and PVC decking: follow manufacturer specs — typically 1/8 to 3/16 inch. Deviating from specified spacing can void the warranty and cause edge mushrooming at fasteners.

Hardwood decking (ipe, tigerwood): 1/8 inch is typical. Dense tropical hardwood moves less than softwood but still needs room for thermal expansion in direct sun.

Effective board module equals actual board width plus gap, converted to feet. Example: 5.5-inch board plus 0.25-inch gap equals 5.75 inches, or 0.479 feet per row module.

Linear feet of decking equals deck area in square feet divided by board module in feet. A 12×16 deck (192 sq ft) with the example module needs about 401 linear feet before waste.

Add 10 percent waste for straight runs — more if the deck has many cutouts, angles, or stairs. Round up to the next full board length available at your supplier to minimize seams.

Stagger butt joints across joists — never align end joints on consecutive rows. A common pattern offsets joints by at least two joist spaces for structural and visual reasons.

Choose board lengths that minimize waste on your deck dimensions. A 12-foot-wide deck may work well with 16-foot boards run lengthwise, while a 10-foot depth may favor 12-foot boards with fewer cuts.

Calculate linear feet first, then convert to board count by dividing by your chosen board length. Buying all one length simplifies ordering but may waste more than mixing lengths.

Hidden clip systems require a specific edge gap and often a starter clip at the house wall. Order 10 to 15 percent extra clips — they break during install and manufacturers specify clips per square foot.

Face screws allow adjustable spacing but need pre-drilling on hardwood and composite to prevent splitting. Two screws per joist crossing is standard; use joist spacing (usually 16 inches on center) to estimate fastener count separately from board linear feet.

Whether you use clips or screws, include the gap in your linear foot estimate. The Deck Calculator accepts board width and gap as inputs for this reason.

Install boards when moisture content is typical for your climate if using natural wood. Wet boards installed with a tight gap will open up as they dry — sometimes more than planned.

Composite boards expand and contract with temperature more than moisture. Install in moderate temperatures when possible, and follow the manufacturer's end-gap requirements at board ends abutting walls or trim.

Check board ends for square before installing. Cumulative error from slightly long boards reduces the gap on the last few rows — plan the final row width before you reach it.

• Calculating board count using nominal width only and ignoring the gap between boards.
• Using the same gap for wet pressure-treated boards as for kiln-dried composite.
• Ordering exact linear feet with zero waste, then coming up short on the last row.
• Forgetting that picture-frame borders and stair treads add linear feet beyond the main field.
• Mixing board widths on the same surface without recalculating module coverage.
• Installing composite without checking manufacturer gap requirements.