Deck Calculator: Decking Square Footage & Boards

Most decking boards are 5.5 inches wide (nominal 6 inch) with a 1/4 inch gap. So each linear foot of board covers about 0.48 sq ft of deck. A 200 sq ft deck needs roughly 416 linear feet of boards, divided by your board length.

For a 12 ft long deck using 12 ft boards, the math is easy. For deck dimensions that aren’t board-length friendly, you’ll have butt joints — and those add 5–10% waste.

Composite decking is sold by the linear foot — calculate exact lengths needed plus 10%. Pressure-treated wood is sold by the board, so you may have to round up to standard 8/10/12/16 ft lengths.

Don’t forget framing: joists, beams, and ledger boards aren’t in your decking sq ft, but they’re a major cost. Get a separate framing estimate.

Deck boards are typically 5.5 inches wide (after the standard 1/4-inch gap between boards) and come in lengths from 8 to 20 feet. To calculate boards needed, divide deck width by board width:

12 ft wide deck with 5.5-inch boards: 12 × 12 ÷ 5.5 = 26.2 board widths needed. Round up to 27 boards.

Deck length determines board length: ideally one continuous board per row. 16 ft long deck = order 16-ft boards. 20 ft deck = order 20-ft boards or accept butt joints.

Total board feet for 12 × 16 deck: 27 boards × 16 ft = 432 linear feet of decking. At 5.5-inch board width that's 432 × (5.5/12) = 198 sq ft of board surface (close to the 192 sq ft of deck area, accounting for the small gap).

Composite decking is sold by the linear foot, hardwood and pressure-treated by the board (length × width × thickness specified). Always specify both linear feet AND square footage when ordering — vendors quote both depending on the product.

Square footage tells you what to price. Board count tells you what to load on the truck. A nominal 2×6 or 5/4×6 deck board is 5½ inches wide, and once you leave a ⅛-inch drainage gap each row covers 5⅝ inches — 0.469 ft. Divide your deck area by that and you get linear feet of decking.

The table assumes boards run the long way, a ⅛-inch gap, and 10% waste for cuts, butt joints and the odd cupped board you set aside. Sizes are field-verified against the formula: area ÷ 0.469 × 1.10 ÷ board length, rounded up to whole boards.

Worked example — a 12 × 16 ft deck. 12 × 16 = 192 sq ft. 192 ÷ 0.469 = 410 linear feet of decking. Add 10% waste: 451 linear feet. At 16 ft per board that is 28.2 boards, so you order 29. Buy them from one lot: pressure-treated stock from different batches can dry to visibly different colours.

Two things the board count does not include. Fascia and picture-frame borders add boards without adding deck area, and a diagonal layout pushes waste from 10% toward 15% because every board meets the rim at an angle.

Deck building involves substantially more lumber than just the visible boards. The framing under the deck consumes 50-70% of the total lumber budget.

Joists: typically 2×8 or 2×10 boards spaced 16 inches on center. For a 12 ft wide deck: 12 × 12 / 16 = 9 joists needed. Each joist is the length of the deck (16 ft for a 12×16 deck). Total: 9 × 16 = 144 linear feet of joist material.

Beams: typically doubled 2×10s or 2×12s. For a 12 ft deck: usually 2 beams running the 12 ft direction, each made of two 12 ft boards = 4 boards × 12 ft = 48 linear feet of beam material.

Posts: 4×4 or 6×6 verticals from concrete footings to beams. Typically 4 corner posts + 1 mid-run post per 6-8 ft of beam length. A 12 × 16 deck needs 6-8 posts.

Joist hangers, post brackets, lag bolts, deck screws: $200-500 in fasteners for a typical deck.

Total deck cost swings more on material choice than on size. The ranges below are fully installed — boards, fasteners, framing labour and all. They are 2026 US planning estimates and move by region and by how much structure sits under the deck; a ground-level platform and a second-storey deck with stairs are not the same job at the same price.

Read the lifespan column alongside the price. Pressure-treated is the cheapest way to get a deck and the most expensive way to keep one, because it wants cleaning and re-staining every couple of years. Composite and PVC cost more up front and ask for almost nothing afterwards.

A paver patio is measured exactly like a deck — length × width for the surface — but ordered in pieces rather than boards. Pavers are sold by the piece or the pallet, and the count per square foot is pure arithmetic: divide 144 by the paver's face area in square inches.

Worked example, a 16 ft × 12 ft patio: 192 sq ft measured. Pavers take a 10% allowance for edge cuts and the occasional breakage, so order against 212 sq ft. In 4 × 8 in pavers that is 212 × 4.5 = 954 pieces. In 12 × 12 in slabs it is 212, because a 12 × 12 paver is exactly one square foot.

Then there is what goes underneath, which is a volume rather than an area and is where paver budgets get missed. Compacted base and bedding are ordered in cubic yards: area × depth in feet ÷ 27. For that same 192 sq ft patio at 4 inches of base, 192 × 0.333 ÷ 27 = 2.37 cubic yards. A deeper base multiplies straight through — at 8 inches it is 4.74.

Cutting waste climbs with the pattern, for the same reason it does with tile. A running bond laid parallel to the edges cuts one row; a 45° herringbone cuts every piece along every edge, and 10% stops being enough.

The square footage above buys the pavers. It does not buy the three things underneath them, and those are measured in different units — which is why a paver patio priced off area alone comes in low.

Worked example on a 12 × 16 ft patio, 192 sq ft. The pavers follow the area. The base is a depth: 4 in of compacted gravel over 192 sq ft is 192 × 4 ÷ 12 = 64 cubic feet, or 2.37 cubic yards. The bedding layer is another depth: 1 in of sand is 16 cubic feet, 0.59 cubic yards. The edge restraint follows the perimeter — 2 × (12 + 16) = 56 linear feet. One measured rectangle, four different units.

A driveway is the same shape and a different job, because the base carries the load rather than the pavers. Where a patio takes 4 in of gravel, a driveway commonly takes 8 to 12; at 10 in the same 192 sq ft needs 5.93 cubic yards of base rather than 2.37. That is the single biggest cost difference between the two, and it is invisible in the square footage.

Then there is the fall. A paved surface has to shed water away from the building, and the usual figure is a quarter inch per foot — about 2.1 percent. Across the 16 ft dimension of this patio that is 4 in of drop from the house to the far edge. It does not change the area by any amount worth measuring, but it does change the excavation depth at one end, and it is the detail that decides whether the patio drains or ponds.

Excavation is base depth plus bedding plus paver thickness, measured down from the finished level you want. Get that wrong and the finished patio sits proud of the door threshold — a mistake that is only fixable by lifting everything and starting at the base.