How to calculate decking boards
Each board covers its own width plus the gap. Divide the deck area by that effective coverage to get the total linear feet of decking, then divide by the board length:
Linear feet = Deck area ÷ ((board width + gap) ÷ 12)
Boards = Linear feet (with waste) ÷ board length
A 16 × 12 ft deck is 192 sq ft. With 5.5-inch boards and a 1/8-inch gap, that's about 410 linear feet, or roughly 57 eight-foot boards after 10% waste.
Gaps and waste
- Gap: about 1/8 inch for dry boards; near-tight for wet pressure-treated lumber that will shrink.
- Waste: 10% for straight decking, 15%+ for diagonal or herringbone layouts.
This covers the surface only
The figure is for decking boards — the walking surface. Joists, beams, posts, footings, and fasteners are separate and depend on your span and local code. Plan the structure with a framing reference or a contractor.
Frequently asked questions
How many deck boards do I need?
Divide the deck area by the coverage of one board (board width plus the gap, times board length) and round up, then add waste. A 16 ft × 12 ft deck is 192 sq ft; with 5.5-inch boards and a 1/8-inch gap, that is about 410 linear feet, so roughly 57 eight-foot boards including 10% waste.
What gap should I leave between deck boards?
About 1/8 inch (0.125 in) is common for boards that are already dry, allowing drainage and a little movement. Pressure-treated boards that are still wet may be butted nearly tight, since they shrink as they dry. The gap effectively widens each board for coverage purposes.
How much extra decking should I buy?
Add about 10% for straight decking to cover cuts and the occasional bad board, and 15% or more for diagonal or herringbone patterns, which waste more at the angled cuts. Picture-frame borders also add a bit.
Does this include the frame and joists?
No — this estimates the decking boards (the surface) only. The substructure of joists, beams, posts, and footings is a separate calculation based on your span and local code. Plan those with a framing guide or a contractor.
Disclaimer: Results estimate decking boards only and assume a simple rectangular deck. Confirm quantities for angled layouts, borders, and the substructure separately.