Deck Board Calculator (Linear Feet & Boards)
Enter your deck's length and width, the actual face width of your boards, the gap you leave between them, and the length of the boards you plan to buy. This calculator returns the deck area, the total linear feet of decking, the number of boards to purchase after a waste allowance, and the material cost. It sizes the surface only — joists, beams, and fasteners are separate.
Deck & boards
Order & cost
Boards to buy
28
400.7 linear ft ÷ 16-ft boards, +10% waste
Deck area
192 ft²
Total material cost
$336.00
Estimate detail
Area · linear ft · boards · cost
How it works
First the deck area is length × width in square feet. Then each board is treated as covering a strip of deck equal to its face width plus one gap: coverage per linear foot = (board width + gap) ÷ 12, in square feet. Dividing area by that coverage gives the total linear feet of board material the surface requires. The gap matters here because it is empty space — a wider gap means each board spans slightly more of the deck, so a little less board material is needed.
Nominal board sizes are not their real face width. A "6-inch" composite or 5/4×6 wood deck board is milled to about 5.5 inches actual; a "4-inch" board is roughly 3.5 inches. Enter the actual width printed on the product spec, not the nominal name, or your board count will run short. The default 0.25-inch gap is a common starting point, but the right gap depends on your material and its moisture content at install.
Linear feet are converted to whole boards by dividing by your board length and multiplying by one plus the waste percentage, then rounding up — you cannot buy a fraction of a board. The default 10 percent waste covers offcuts, miters, defective boards, and the seams that fall where a board length does not divide evenly into a run. Total cost is simply the board count times the price you enter per board.
Frequently asked questions
Why leave a gap between deck boards at all?+
The gap serves drainage and expansion. It lets rain drain through the surface instead of pooling on the boards, and it gives the material room to move as it swells and shrinks with moisture and temperature. Pressure-treated wood is often installed wet and shrinks as it dries, so some builders butt those boards nearly tight knowing a gap will open up later; kiln-dried wood and composites are usually spaced with a fixed gasket or gap. Always follow your specific product's installation guide — the right gap is a material-specific number, and this calculator simply uses whatever gap you enter.
How does board length change how many boards I need?+
Board length affects waste and seams, not the total linear feet of material. If your board length divides evenly into your deck run, you get almost no offcut waste; if it does not, every row ends in a short leftover piece that may be too small to reuse, and you get a seam wherever two boards meet end to end. Longer boards mean fewer seams but pricier, harder-to-handle stock and potentially more waste per row. This tool applies your flat waste percentage rather than simulating each row, so treat the board count as a solid estimate and confirm the layout of your specific run before ordering.
Does this include hidden fasteners or the substructure?+
No. The calculator sizes the visible deck surface only. It does not model fastening — hidden fasteners versus face screws change your hardware order and your board spacing, and grooved boards for hidden clips behave differently from square-edge boards you screw through the face. It also excludes joists, beams, posts, railing, stairs, and fascia. Use it to estimate decking material and cost, then size the substructure and fasteners separately from your framing plan and your fastener manufacturer's coverage chart.