Deck Board Calculator
Count the decking for a rectangular deck. Enter the deck size, board width, the gap between boards, and the stock length, and get the number of boards, the rows, and the linear feet — with waste sized to your layout.
The direction the boards run.
Across the boards.
Actual board width — nominal 6-in decking is about 5.5 in.
Picking a layout sets a suggested waste — raise it for lots of cuts.
Advanced: price
Formula & how it works
Rows across = deck width × 12 ÷ (board width + gap), rounded up. Boards per row = deck length ÷ board length, rounded up.
Boards = rows × boards per row × (1 + waste), rounded up. Linear feet = rows × deck length × (1 + waste).
Worked example
A 16 ft long, 12 ft wide deck with 5.5 in boards and a 1/4 in gap needs 26 rows (144 in ÷ 5.75 in). With 16 ft boards that's one board per row, so 26 before waste; at 10% straight-layout waste, round up to 29 boards — about 458 linear feet. Switch to 12 ft boards and each row needs two, pushing it to 60 boards.
Estimating decking
Rows come from width, boards come from length
The number of rows depends only on how wide the deck is and how much space each board plus its gap takes. How many boards make up each row depends on the deck's length against the stock length you can buy. Longer boards that span the whole deck mean one board per row and the least waste; shorter boards force a seam and a second piece per row.
Mind the gap
The gap between boards matters more than it seems — over a wide deck, a bigger gap removes whole rows. Wood installed wet is often butted tight because it shrinks; dry lumber and composite are spaced with a consistent gasket. Use your actual planned gap here rather than a default.
Layout drives the waste
A straight layout cuts cleanly and wastes little. A diagonal run leaves angled offcuts at both ends of nearly every board, so it needs a bigger margin, and a picture-frame border adds mitered corner cuts. This estimate leans slightly generous because it counts each row's boards separately, but offcuts from one row can often start the next — so treat the number as a comfortable buy, not a floor.