Deck Board Calculator

How to Use the Deck Board Calculator

Enter your deck's length and width in feet, your deck board's width and the gap you're leaving between boards (both in inches), and a waste factor for cuts. The calculator returns your total deck area and the number of boards to order.

How the Calculation Works

The calculator figures out how many rows of decking span the deck's width by dividing the width (in inches) by the combined board width plus gap — each row takes up that much space across the deck. It rounds up to a whole row, then adds your waste percentage for cuts and seams, and rounds up again to a whole board.

Example Calculation

A 16×12 ft deck using 5.5-inch-wide boards with a 0.25-inch gap and 10% waste: rows = ceil((12 × 12) ÷ (5.5 + 0.25)) = ceil(144 ÷ 5.75) = ceil(25.04) = 26. Boards = ceil(26 × 1.10) = 29.

Frequently Asked Questions

Does this assume boards run the full length of the deck?

Yes — this calculator estimates the number of board-widths needed to span the deck, assuming full-length runs. If your deck is longer than standard board lengths (commonly 12 or 16 ft) and needs seams, you may need additional boards to stagger those joints.

What gap should I leave between deck boards?

A 1/8" to 1/4" gap is typical for wood decking to allow for drainage and seasonal expansion. Composite decking often has different manufacturer-specified gap requirements — check your product's installation guide.

How much waste factor should I use for decking?

10% is a reasonable default for a simple rectangular deck. Decks with diagonal board patterns, curves, or lots of cutouts (for posts, stairs) typically need a higher waste allowance.