How Many Deck Boards Do I Need?
Part of Decks, Fences & Roofing
Quick answer
Divide the deck width by one board's coverage (its face width plus the gap between boards) to get the number of rows, multiply by the deck length for total linear feet, add about 10% for waste, then divide by your board length. A 16 × 12 ft deck in 5.5-inch boards needs roughly 26 rows — about 29 sixteen-foot boards once you add waste.
Decking is sold by the board, but you size it by coverage. Each board covers its face width plus the small drainage gap, so the count comes down to how many of those strips fit across the deck, times how long each run is.
The steps
- Rows across the deck = deck width (in) ÷ (board face width + gap), rounded up. A 2×6 board is 5.5 in wide; add 1/8 in gap.
- Total decking = rows × deck length (ft).
- Add waste: 10% straight, 15% for diagonal layouts.
- Boards = total decking ÷ your board length (e.g. 16 ft), rounded up.
Boards per deck (5.5 in board, 16 ft long, 10% waste)
| Deck size | Area | ≈ 16 ft boards |
|---|---|---|
| 10 × 10 ft | 100 ft² | ~16 |
| 12 × 12 ft | 144 ft² | ~22 |
| 16 × 12 ft | 192 ft² | ~29 |
| 20 × 16 ft | 320 ft² | ~49 |
Match your board length to the deck length to cut waste — a 16 ft deck framed for 16 ft boards has almost no offcuts. The deck calculator does the full math and adds joists and screws.
FAQs
How many deck boards are in a square foot?
A 5.5-inch board with a 1/8-inch gap covers about 0.47 linear feet of width per foot of length — roughly 2.1 linear feet of board per square foot of deck. For quick math, a 100 ft² deck takes about 210 linear feet of decking before waste.
Should deck boards run the length or width?
Either, but boards must run perpendicular to the joists. Running them the long way looks cleaner with fewer butt joints; running them across can use shorter, cheaper boards. Diagonal decking needs joists at 12 inches on center and adds about 15% waste.