How to Calculate the Board Feet Needed for a Tropical Hardwood Deck From Square Footage

What a Board Foot Is

A board foot is the standard unit lumber is measured and estimated in, equal to 144 cubic inches, or a piece one inch thick by twelve inches wide by one foot long. It is a volume measure, calculated as nominal thickness in inches times nominal width in inches times length in feet, divided by twelve. For decking sold and estimated by the board foot, converting a deck's area into board feet is what lets a supplier quote and fill the order. The National Hardwood Lumber Association defines the measurement conventions lumber follows. Our board feet guide covers the unit in depth.

Square Feet, Linear Feet, and Board Feet Are Different

A deck's size is a square-footage area, but decking is installed as linear feet of board and estimated as board feet of lumber, so the calculation moves through all three. Square footage is the deck's plan area. Linear feet is the total length of board needed to cover that area, which depends on how much face each board covers. Board feet is the volume unit that accounts for the board's thickness and width. Confusing these is a common source of ordering errors, since one square foot of deck is not one board foot of lumber.

Coverage: Actual Width Plus the Gap

Coverage is figured from the board's actual milled width plus the installed gap, not the nominal size, because a nominal 6-inch board finishes near 5-1/2 inches and sits with a gap of about 3/16 inch between boards. So a nominal 5/4x6 board covers roughly 5-1/2 inches of face plus 3/16 inch of gap, about 5.69 inches, or 0.474 feet, of deck width per board run. Using the nominal 6 inches instead would under-order, because the boards actually cover less. The USDA Forest Products Laboratory documents the nominal-versus-actual milling conventions. Nominal widths promise face the board does not have. With the true coverage width in hand, Step 1 converts the deck area into linear feet.

Step 1: Square Feet to Linear Feet

Divide the deck area in square feet by the coverage width of one board in feet to get the total linear feet of board needed. For a 200-square-foot deck using 5/4x6 boards that cover 0.474 feet each, that is 200 divided by 0.474, or about 422 linear feet of board before waste. This is the length of board that will actually be fastened down. If the deck uses a different width, the coverage changes, so narrower boards need more linear feet and wider boards need fewer. That 422 feet is a bare minimum, and no real deck installs at the bare minimum, which is exactly what Step 2 corrects.

Step 2: Add a Waste Factor

Add a waste factor, typically 10 to 15 percent, to cover cutting to length, angled cuts, defects trimmed out, and breakage, so the crew does not run short. On a simple rectangular deck, 10 percent is often enough; on a deck with angles, a picture-frame border, or a complex layout, 15 percent or more is prudent. For the 422 linear feet in the example, a 12 percent waste factor brings it to about 473 linear feet ordered. Ordering to a cut list lets a supplier optimize lengths and tighten the waste factor, since matched long lengths reduce drop. Skimping on waste just moves the shortage to mid-install. In practice, J. Gibson McIlvain runs this coverage and waste math with the buyer and fills the order to the cut list from deep inventory, so the number quoted and the load delivered match. With the waste folded in, Step 3 converts those linear feet into board feet, the unit the order is written in.

Step 3: Linear Feet to Board Feet

Convert linear feet to board feet using the board's nominal thickness and width: board feet per linear foot equals nominal thickness times nominal width divided by twelve. For a 5/4x6 board, that is 1.25 times 6 divided by 12, or 0.625 board feet per linear foot. So about 473 linear feet times 0.625 is roughly 296 board feet of 5/4x6 to order. This board-foot figure is what a supplier quotes and fills. The American Wood Council references these conventions in its design and material documentation. Stacked together, the three steps run as one pass, which the worked example below shows end to end.

Worked Example: Board Feet for a 200 sq ft Deck

For a 200-square-foot deck in 5/4x6 tropical hardwood: coverage 0.474 ft per board, so about 422 linear feet; plus 12 percent waste, about 473 linear feet; times 0.625, about 296 board feet. The same deck in a narrower 5/4x4 board would need more linear feet because each board covers less face, while a wider board would need fewer. Running the numbers for the actual board width chosen is what makes the order accurate. See our Ipe vs. Cumaru guide for how board choice interacts with cost. The board-foot total does one more job before ordering: it tells you what the delivery weighs.

Decking Weight and Delivery

Board feet also indicate the order's weight, which matters for delivery and for a rooftop or balcony's structural load: dense tropical hardwood runs roughly 5 to 6 lb per square foot installed for 5/4 Ipe. A 200-square-foot Ipe deck is therefore on the order of 1,000 to 1,200 lb of decking, which shapes how it ships and, on a raised structure, whether the frame carries it. Kiln-dried tropical hardwood near a density of 1,050 kg/m3 is heavy, so the board-foot total is a proxy for the logistics as well as the material.

Ordering to a Cut List, Not Just a Total

The most accurate order is a cut list of the actual board lengths the deck needs, not just a board-foot total, because it lets the supplier optimize lengths to minimize drop and jointing. A board-foot total tells the supplier how much wood; a cut list tells them which lengths, so they can pull long boards for long runs and reduce both waste and butt joints. On premium tropical hardwood, that optimization is worth real material. J. Gibson McIlvain fills orders to a cut list from deep inventory, kiln-dried and graded, shipping nationwide.

Adjusting for Board Width, Diagonal, and Pattern Layouts

The board width and the layout pattern change both the coverage and the waste factor, so a diagonal or patterned deck needs a higher waste allowance than a straight one. A narrower 5/4x4 board covers less face than a 5/4x6, so it needs more linear feet for the same area; a wider board needs fewer. Laying boards on a diagonal, in a herringbone, or with a picture-frame border increases cutting and drop, pushing the waste factor toward 15 percent or higher rather than 10. Running the coverage math for the actual board width chosen, and raising the waste factor for the pattern, is what keeps a patterned order accurate. The International Code Council codes govern the structural layout the boards span. Diagonals and borders eat boards. Budget the waste accordingly.

Estimating Fasteners, Clips, and Plugs

Beyond the wood, an order includes the fasteners, and their count follows from the board layout: roughly two fasteners per board at each joist. For face-screwed decking, that is two stainless screws per board per joist, so the screw count rises with the number of joists and boards, and plugged decks need a matching plug per screw. Hidden-clip decks use one clip per board edge per joist, plus starter clips at the perimeter. Estimating the fasteners with the wood ensures the deck ships complete. J. Gibson McIlvain can include the matched stainless fasteners, clips, and plugs sized to the board and joist layout with the order.

Board-Foot Conversion Reference

A board foot is 144 cubic inches; the per-linear-foot factor is nominal thickness times nominal width divided by twelve, following NHLA measurement rules and the milling conventions documented by the USDA Forest Products Laboratory.

"People ask how much wood a deck takes and expect square feet to equal board feet, but they are not the same. You go from the deck area to linear feet using what the board actually covers, add waste for cuts and defects, then convert to board feet to order. The single best thing a customer can do is give us a cut list instead of a footage number, because then we optimize the lengths and they are not paying for drop or jointing every few feet."

Camden Zacker, Sales Director, J. Gibson McIlvain Company