Decking Calculator
Estimate how many deck boards you need — enter your deck dimensions, board size, and spacing.
Results update instantly as you type.
Interactive Deck Layout
Visualization updates as you enter dimensions above.
How Many Deck Boards Do I Need?
To calculate how many deck boards you need, divide the deck width by the effective board width (board width + gap), then multiply by the number of board lengths needed to span the deck length.
The decking formula is:
Boards = ⌈(Deck Width ÷ (Board Width + Gap)) × (Deck Length ÷ Board Length)⌉ + Waste %
1
Measure the Deck Area
Measure the total length and width of your deck in feet.
2
Know Your Board Size
Standard deck boards are 5.5 inches wide and 8, 12, or 16 feet long.
3
Set Your Gap Spacing
Leave 1/8″ for wood, 3/16″ for composite. Gaps allow drainage and expansion.
4
Add Waste Factor
Add 10–15% for straight layouts. Diagonal or herringbone patterns need 15–20%.
What Are Standard Deck Board Sizes?
| Board Size | Actual Width | Common Lengths | Material |
|---|---|---|---|
| 5/4 × 6 | 5.5 in | 8, 10, 12, 16 ft | Pressure-treated, cedar |
| 2 × 6 | 5.5 in | 8, 10, 12, 16 ft | Pressure-treated pine |
| Composite | 5.5 in | 12, 16, 20 ft | Trex, TimberTech |
| 1 × 6 | 5.5 in | 8, 12 ft | Cedar, redwood |
Frequently Asked Questions
How many deck boards do I need for a 12×16 deck?
A 12×16 ft deck needs approximately 35–40 standard 5.5″ deck boards (8 ft length), depending on spacing and waste factor. Use our calculator above for an exact count.
How much gap should I leave between deck boards?
Leave 1/8 inch (3mm) gap between wood deck boards. For composite decking, follow manufacturer specs — usually 3/16 to 1/4 inch. Gaps allow water drainage and wood expansion.
How do I calculate deck board feet?
Multiply the number of boards by the board foot formula: Board Feet = Length (ft) × Width (in) × Thickness (in) ÷ 12. For a standard 5/4×6×8, that’s 5.5 BF per board.
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