How to Calculate Deck Boards
Calculating the number of decking boards is a matter of dividing your deck area into rows and columns. The boards run along the length of the deck, and you need enough rows side by side to cover the width. The key variable most people forget is the gap between boards — the small space that allows water drainage and wood expansion.
Boards = Rows × (Deck Length ÷ Board Length) × (1 + Waste)
The standard board gap is 1/8 inch for wood decking. Composite manufacturers often specify 3/16 inch or use proprietary hidden fastener systems that set the gap automatically.
Choosing a Board Length
Decking boards come in standard lengths: 8, 10, 12, 16, and sometimes 20 feet. The most cost-effective approach is to choose a board length that matches or slightly exceeds your deck length, so each row is a single board with minimal waste. If your deck is 14 feet long, 16-foot boards leave only 2 feet of waste per board. Using 12-foot boards would require a butt joint in every row, creating more cuts and waste.
Decking Board Sizes
| Nominal | Actual Width | Common Use |
|---|---|---|
| 5/4×6 | 5.5" | Most common residential decking |
| 5/4×4 | 3.5" | Narrower boards for a different aesthetic |
| 2×6 | 5.5" | Heavier duty, commercial or high-traffic |
| Composite | 5.5" or 7.25" | Varies by manufacturer |
Deck Board Costs by Material
| Material | Per Linear Ft | Per Sq Ft (installed) |
|---|---|---|
| Pressure-treated pine (5/4×6) | $0.75–$1.50 | $2–$5 |
| Cedar (5/4×6) | $2.00–$4.00 | $5–$10 |
| Composite (mid-range) | $2.50–$4.50 | $8–$12 |
| Composite (premium) | $4.00–$6.50 | $12–$18 |
| PVC (Azek, TimberTech) | $5.00–$8.00 | $14–$22 |
How to Minimize Waste
The biggest source of waste in decking is offcuts from board ends. Three strategies reduce this: design your deck dimensions to match standard board lengths when possible; stagger butt joints so offcuts from one row become starters for the next; and order a mix of board lengths if your supplier carries them, giving more flexibility to minimize cuts.