How This Calculator Works
Decking is ordered by board count and length, not just square footage. This calculator estimates board courses across the deck width and total linear feet to buy.
Formula
Board courses = deck width / (board face width + gap). Linear feet = courses x deck length + picture-frame length. Boards = linear feet / board length, rounded up.
Assumptions
The default board face is 5.5 inches with a 1/8 inch gap and 12 ft boards. Picture-frame borders, stairs, diagonal decking, and seam layouts can change the order.
Measurement Checklist
- Use actual board face width, not the nominal board size.
- Enter the planned gap because it changes the number of board courses.
- Add picture-frame or border boards as linear feet instead of burying them in square footage.
- Estimate framing, railing, stairs, posts, fasteners, and footings separately.
Practical Examples
- A 16 ft by 12 ft deck using 5.5 inch boards, 1/8 inch gaps, 12 ft board lengths, and 10% waste needs about 39 deck boards.
- A 12 ft by 12 ft deck with 5.5 inch boards, 1/8 inch gaps, 12 ft boards, and 10% waste needs about 29 boards.
- A 20 ft by 14 ft deck with 16 ft boards and 10% waste needs about 54 boards before stairs, railing, and picture-frame trim.
- Adding 56 linear feet of picture-frame border to a 16 ft by 12 ft deck with 10% waste increases the estimate from about 39 to about 44 twelve-foot boards.