Decking Calculator
Find how many deck boards you need from the deck size, board width, board length and a waste allowance.
How it works
deck area = length × width · board coverage = (board width ÷ 12) × board length · boards = ceil(deck area ÷ board coverage × (1 + waste%))
Each board covers its face width (converted from inches to feet) times its length, so dividing the deck area by one board’s coverage gives the raw board count. Adding the waste allowance and rounding up covers cuts, defects and the gaps between boards, which the simple area math ignores. Ten percent suits a straight layout; add more for diagonal or picture-frame designs that generate more offcuts.
Worked example
A 16 × 12 ft deck is 192 ft². A 5.5 in × 16 ft board covers (5.5 ÷ 12) × 16 ≈ 7.33 ft². 192 ÷ 7.33 = 26.2 boards; with 10% waste that rounds up to 29 boards, about 464 linear feet.
Frequently asked questions
Does this include the gap between boards?
The waste allowance absorbs the small drainage gap (about 1/8 in) along with cuts and defects. For a precise take-off, add the gap to the board width before dividing, but for ordering, the 10% margin covers it comfortably.
Which way should the boards run?
Perpendicular to the joists. Running boards diagonally looks striking but wastes more material — bump the allowance to 15% — and needs joists spaced closer to keep the boards stiff underfoot.
How do I handle a picture-frame border?
A border around the perimeter adds mitered cuts and short offcuts, so add 15% rather than 10% and buy a couple of extra long boards. Plan the border width first, then field the interior boards into the remaining space.
Related calculators
Estimate for planning. Add a waste margin and confirm with your supplier and local codes.