Most composite deck boards measure 5.5 inches wide, roughly 1 inch thick, and come in 12-foot, 16-foot, or 20-foot lengths. But those numbers only tell part of the story. Board profiles, core types, and edge options vary across brands and product lines, and picking the wrong size can mean mismatched boards, wasted material, or a deck that doesn't meet code.
We've put together this guide to help you find the exact composite decking dimensions for your project, whether you're building from scratch, replacing damaged boards, or comparing products across manufacturers.
Quick Reference: Standard Composite Deck Board Dimensions
| Width: | 5.5 inches (standard) | 3.5 to 7.25 inches available depending on brand |
| Thickness: | 0.94 to 1.1 inches (varies by product line and core type) |
| Lengths: | 12 ft, 16 ft, 20 ft (20 ft may be special order) |
| Edge Options: | Square edge (visible edges, face-screw install) or Grooved edge (hidden fastener install) |
| Core Types: | Solid core (maximum strength) or Hollow/scalloped core (lighter weight, lower cost) |
Standard Composite Deck Board Dimensions
Composite Deck Board Width Options
The standard composite deck board width is 5.5 inches (actual measurement), which corresponds to the nominal "6-inch" board you'd see in lumber terminology. This is the most common width across every major manufacturer, including TruNorth, Trex, TimberTech, and Fiberon.
For most standard deck builds, 5.5-inch boards are the right call. They balance visual proportion, structural performance, and material efficiency. Wider boards cover ground faster but expand and contract more with temperature changes, which means you'll need to be more precise with your gap spacing.
Standard Deck Board Lengths
Composite deck boards are sold in three standard lengths: 12 feet, 16 feet, and 20 feet. Most retailers stock 12-foot and 16-foot boards. The 20-foot option is available from brands like TruNorth.
Longer boards reduce the number of end-to-end seams on your deck surface, which looks cleaner and reduces the number of joints you need to support with doubled joists. But they're heavier and harder to handle during installation, especially if you're working without a crew.
For a standard residential deck, 16-foot boards offer the best balance between coverage and handling. Composite decking cuts easily with standard woodworking tools, so you can trim any board down to the length you need. Make sure not to install boards end-to-end, but have a perpendicular trim board in between to avoid buckling of the boards when they expand in warmer weather.
Composite Deck Board Dimensions Compared by Brand
One of the biggest frustrations we hear from homeowners is that it's hard to compare products across brands. So we built a side-by-side comparison table with actual dimensions from each manufacturer's specifications.
| Brand / Product | Width | Thickness | Lengths | Core Type | Edge Options |
| Trex Transcend | 5.5" | 1.0" | 12', 16', 20' | Solid | Square & Grooved |
| Trex Enhance | 5.5" | 0.94" | 12', 16', 20' | Scalloped | Square & Grooved |
| TimberTech PRO Legacy | 5.5" | 1.0" | 12', 16', 20' | Solid | Square & Grooved |
| TimberTech Vintage | 3.5", 5.5", 7.25" | 1.0" | 12', 16' | Solid | Square & Grooved |
| TruNorth Accuspan Gen II | 5.5" | ~1.0" | 12', 16', 20' | Solid | Square & Grooved |
| TruNorth Enviroboard | 5.5" | ~1.0" | 12', 16', 20' | Hollow | Square & Grooved |
| Fiberon Concordia | 5.5" | 0.94" | 12', 16', 20' | Scalloped | Square & Grooved |
All of these products are available in both grooved edge (for hidden fastener installation) and square edge (for face-screw installation or visible edges). Always confirm the exact dimensions with the retailer before ordering, because manufacturers do update specifications between product generations.
One thing worth noting: TruNorth's composite boards use rice husks instead of wood fibers as their organic component. This doesn't change the board dimensions, but it does affect density and weight. Rice husk boards are harder and more scratch-, mold-, and fire-resistant than wood-fiber composites at the same thickness, which is worth knowing if you're comparing boards that look similar on a spec sheet. Additionally, TruNorth boards are reversible, unlike scalloped boards.
Solid Core vs. Hollow Core Composite Deck Boards
The cross-section profile of a composite deck board is just as important as its length and width. Understanding the difference between solid core and hollow core boards helps you pick the right product for your specific application.
When Solid Core Makes Sense
Solid core boards have a dense, uniform cross-section with no internal voids. They're heavier, stronger, and better suited for high-traffic areas, commercial applications, and decks built at grade level where debris might accumulate underneath. They also come in a square edge profile, good for trim and stairs.
Products like TruNorth Accuspan Gen II use a solid core construction with 4-sided capping, meaning the protective shell wraps around every exposed surface. Trex Transcend and TimberTech PRO Legacy also use solid profiles. These boards handle point loads well, resist furniture indentation, and work for stairs where the board edge is exposed and visible.
Best for: New deck construction, high-traffic residential, commercial, stairs, and areas with heavy furniture or grills.
When Hollow Core Makes Sense
Hollow core (or scalloped bottom) boards have internal channels or ridges that reduce weight and material cost. They're easier to carry, cut, and install, which makes them a strong option for DIY projects and upper-level deck renovations where you'd rather not add excessive structural load.
TruNorth Enviroboard, for example, uses the same 4-sided rice husk capping as the Accuspan line but with a hollow core profile. It's lighter and more affordable while still carrying a 25-year warranty. Trex Enhance uses a scalloped bottom profile with the same idea: reduce material without sacrificing surface durability.
Best for: Budget-conscious projects, DIY installation, deck renovations, and upper-story decks.
The key thing: both solid and hollow boards use the same capping technology on the surface you walk on. The difference is underneath, in the structural core. For most residential decks, either option works fine as long as your joist spacing matches the manufacturer's requirements.
Composite Deck Board Profiles and Edge Options
Beyond the overall board dimensions, the edge profile determines how the board installs and where it can be used on your deck.
Square Edge vs. Grooved Edge Boards
Grooved edge boards have a small channel milled into both long sides. This groove accepts hidden fastener clips that snap into the channel and screw down into the joist below. The result is a smooth deck surface with no visible screws. Most composite deck boards sold today are grooved edge, and most manufacturers (including TruNorth with their Slide & Go clips) offer compatible hidden fastener systems.
Square edge boards have flat, smooth sides with no groove. You install them by driving screws through the face of the board into the joist below. The screws are visible on the deck surface, but you can minimize their appearance with color-matched plug systems like the Starborn Pro Plug.
Which Profile Goes Where on Your Deck
Here's the practical breakdown:
- Main deck surface: Grooved edge boards with hidden fasteners for a clean, screw-free look.
- Picture frame border: Square edge boards. The outside edge of the border is exposed, so you need a clean, flat edge.
- Stair treads: Square edge boards. Grooved edges on stairs create a gap that can catch heels and collect debris.
- First and last board: Some installers use square edge for the first board against the house and the last board at the deck edge, face-screwing them for a secure connection.
- Fascia and riser boards: These are separate, thinner boards (typically 0.5 inches thick) designed to cover the exposed face of your deck frame. They're available in matching colors from most brands.
How Composite Decking Dimensions Compare to Traditional Wood
If you're switching from pressure-treated lumber to composite decking, the dimension comparison can be confusing. Traditional wood lumber uses nominal sizing, which means a "5/4 x 6" board doesn't actually measure 1.25 inches by 6 inches. Its actual dimensions are roughly 1 inch by 5.5 inches after milling and drying.
Composite boards are designed to match those actual dimensions, not the nominal names. So a standard composite deck board at 5.5 inches wide and 1 inch thick fits directly onto framing that was designed for 5/4 x 6 lumber. This makes composite boards a direct replacement in most renovation scenarios.
The important exception: some composite product lines run slightly thinner (0.94 inches, for example). If you're replacing only a few boards on an existing deck, check that the new boards match the thickness of the originals. Even a small difference creates an uneven surface.
How Deck Board Dimensions Affect Your Build
Joist Spacing and Board Thickness
Your composite deck board thickness and core type directly determine how far apart you can space your joists. Most composite boards are rated for 16-inch on-center joist spacing when installed perpendicular to the joists. If you're running boards at a 45-degree diagonal pattern, most manufacturers require tighter 12-inch on-center spacing to provide adequate support.
Solid core boards generally handle wider spans better than hollow or scalloped profiles. Always check the manufacturer's installation guide for your specific product. TruNorth, for example, provides detailed span tables in its installation documentation for both the Accuspan and Enviroboard lines.
Estimating Coverage and Material Needs
A standard 5.5-inch wide, 16-foot long composite deck board covers about 7.3 square feet of deck surface (factoring in the recommended 3/16-inch gap between boards). To estimate how many boards you need:
- Calculate your total deck square footage (length x width).
- Divide by the coverage area per board (about 7.3 sq ft for a 16-foot x 5.5-inch board).
- Add 10% for waste from cuts, angles, and mistakes.
- Round up. You always want a couple extra boards on hand.
Choosing wider boards means fewer total boards and fewer fasteners, but it also means more waste if your deck dimensions don't divide evenly into the board width. Narrower boards give you more layout flexibility but take longer to install. On www.compositedeckdirect.com, you can enter your square footage, and all boards and hardware are automatically calculated.
Common Mistakes with Composite Decking Sizes
We've seen these come up repeatedly, and they're all avoidable with a little planning.
Mixing board thicknesses from different product lines. Even boards from the same manufacturer can vary in thickness between collections. If you're patching an existing deck, bring a sample of the original board to your supplier for comparison.
Ignoring the gap between boards. Composite decking expands and contracts with temperature changes. Most manufacturers specify a 3/16-inch gap between boards. Skip this, and your boards will buckle in summer heat. Factor these gaps into your material estimate.
Ordering square edge when you need grooved (or vice versa). Double-check your fastener system before ordering. Hidden clip systems only work with grooved edge boards. If you've already bought square edge boards, you'll need to face-screw them.
Assuming all brands use the same joist spacing. A board from Brand A rated for 16-inch centers might look identical to one from Brand B that requires 12-inch centers. The difference comes down to core construction and material composition. Check the spec sheet.
Forgetting about fascia, riser, and trim boards. Your deck isn't just the walking surface. You'll also need fascia boards to cover exposed framing, riser boards for stairs, and possibly nosing boards for stair treads. These come in their own specific dimensions and should be included in your material order.
FAQ: Composite Decking Dimensions
How wide is a composite deck board?
The standard composite deck board width is 5.5 inches (actual measurement). This matches the actual width of a traditional 5/4 x 6 wood deck board. Some brands offer wider options up to 7.25 inches and narrower boards down to 3.5 inches for multi-width pattern designs.
How thick is composite decking?
Most composite deck boards are between 0.94 and 1.1 inches thick. Solid core boards tend to be at the thicker end of this range, while scalloped or hollow core boards may be slightly thinner. Always verify the exact thickness on the product's specification sheet, especially if you're replacing individual boards on an existing deck.
What is the difference between grooved edge and square edge composite decking?
Grooved edge boards have a channel on each long side that accepts hidden fastener clips, giving you a screw-free deck surface. Square edge boards have flat sides and require face-screwing. Use grooved boards for the main deck area and square edge boards for borders, stairs, and any location where the board edge is exposed.
What is the difference between solid and hollow composite deck boards?
Solid core boards have a dense, uniform interior. They're heavier and stronger, better for high-traffic areas and stairs. Hollow core boards have internal channels that reduce weight and cost while using the same protective capping on the surface. Both types perform well for residential decks when installed per the manufacturer's joist spacing requirements.
Can I mix composite deck boards from different brands on the same deck?
This isn't recommended. Even when two products have similar listed dimensions, small differences in thickness, color, and texture will be visible once installed. Stick with one brand and product line for your entire deck surface. If you're repairing a section, match the original product as closely as possible.
How do I calculate how many composite deck boards I need?
Measure your deck area in square feet (length times width). Divide by the coverage area per board. For a standard 5.5-inch by 16-foot board, that's about 7.3 square feet. Then add 10% for waste from cuts and angles. If your design includes diagonal patterns or complex shapes, bump the waste allowance to 10-15%.
Does composite decking come in the same sizes as wood decking?
Composite boards are designed to match the actual (not nominal) dimensions of standard wood lumber. A composite deck board at 5.5 inches wide and 1 inch thick fits the same framing as a 5/4 x 6 wood board. The main difference is that composite doesn't shrink, warp, or split like wood, so the dimensions stay consistent over the life of the product.
How far apart should joists be for composite decking?
Most composite deck boards require joists spaced at 16 inches on center for perpendicular installation. Diagonal installation typically requires 12-inch on-center spacing. Stair treads often need 9 to 12 inches between stringers. Always follow the specific manufacturer's installation guide for your product, as requirements vary.