Deck Board Calculator

Compute the deck area in square feet. Convert the deck width to inches and divide by the per-board coverage (board width plus gap) to get the number of rows. Divide deck length by board length and round up to get boards per row. Multiply rows by boards per row to get total boards before waste. Apply a waste percent and round up to the final order count.

10 percent is a fair default for a rectangular deck with straight runs. Picture-framed decks, diagonal layouts, or decks with stairs and angled corners typically need 12 to 20 percent. Composite boards in long lengths often waste less than short hardwood boards. The waste percent is added on top of the bare board count before rounding up.

Composite decking typically uses a 1/8 in (0.125 in) gap. Pressure-treated softwood is often gapped at 1/8 to 1/4 in when installed wet (the boards shrink as they dry). Hardwood like ipe is usually gapped 1/8 in. Check the manufacturer's instructions for your specific deck board.

The calculator rounds up boards per row to a whole number, so even a slightly longer board length results in one board per row. You will end up with offcuts that can sometimes be used elsewhere on the deck (stair treads, picture-frame borders) but should not generally be counted toward the row total.

Not specifically. Picture-framing and stairs add boards and waste; bump the waste percent to 15 to 20 percent if you are doing either. For a fully picture-framed deck, add the perimeter trim boards manually based on the perimeter and your trim board length.

The cost line is the final board count times your entered price per board. It does not include joists, posts, hardware, fasteners, railings, stair stringers, finish, delivery, sales tax, or labor. Treat it as a decking-only planning figure.