Deck Board Calculator
Calculate decking boards, rows and linear feet from deck size, board width, gap and board length. Includes waste and cost.
Deck boards needed
29
- Rows of decking
- 26
- Boards per row
- 1
- Total boards
- 29
- Linear feet of decking
- 312 ft
- Estimated board cost
- $435.00
Assumes boards run parallel to the deck length with a 0.25 in gap. Add 10% for cuts and breaks; use more for diagonal or picture-frame layouts.
Deck boards are sold in fixed lengths, and the number you need depends on board width, the gap between boards and how the boards run across the joists. This calculator lays out the rows and converts them into boards and linear feet.
The default assumes boards run parallel to the deck length and are cut at the ends. If you run boards diagonally, add more waste; if you use a picture-frame border, calculate the border separately.
How the deck board calculator works
Each row covers the board width plus the gap, converted to feet. Rows = ceiling(deck width ÷ row coverage). Boards per row = ceiling(deck length ÷ board length). Total boards = rows × boards per row × (1 + waste), rounded up. Linear feet is rows × deck length.
Worked example
A 12 × 12 ft deck with 5.5-inch boards and a 1/4-inch gap has 26 rows. At a 12 ft board length, that is one board per row, or 26 boards before waste — 29 boards with 10% waste.
Board layout and joists
- Deck boards run perpendicular to the joists. Running them diagonally needs more waste and blocking.
- Joists are typically 16 inches on center; composite boards may require 12 inches.
- Leave a 1/8–1/4 inch gap between boards for drainage and expansion. Composite gaps follow the manufacturer.
- Butt joints must land over a joist, and each board end needs two fasteners.
Decking materials
| Material | Upfront cost | Maintenance | Typical life |
|---|---|---|---|
| Pressure-treated wood | Low | Stain every 1–3 years | 15–25 years |
| Composite | Medium–high | Wash periodically | 25–30 years |
| PVC | High | Low | 30+ years |
| Aluminum | High | Very low | 30+ years |
| Hardwood (ipe, cumaru) | High | Oil annually | 25–40 years |
Fasteners and spacing
- Use stainless or coated deck screws, not drywall screws.
- Hidden clips give a clean face but need consistent gaps and a compatible board.
- Two screws per joist per board is standard; some manufacturers require more at the ends.
- Keep fasteners at least 1 inch from the board end to avoid splitting.
Frequently asked questions
How many deck boards do I need for a 12 × 12 deck?
With 5.5-inch boards and a 1/4-inch gap, a 12 ft wide deck needs 26 rows. At a 12 ft board length that is 26 boards, or 29 with 10% waste.
Which direction should deck boards run?
Perpendicular to the joists. Boards are often run parallel to the house for appearance, which means the joists run away from the house. Diagonal layouts need more material and blocking.
What gap should I leave between deck boards?
About 1/8–1/4 inch for wood, enough for water to drain and for seasonal movement. Composite and PVC boards follow the manufacturer's gap specification.
How far apart should deck joists be?
16 inches on center is standard for wood decking. Composite boards often require 12 inches, and some aluminum systems use different spacing. Check the board manufacturer's span table.
Composite or wood decking?
Composite costs more upfront but needs less maintenance. Wood is cheaper and easier to repair but needs staining and can splinter. Consider heat, slip resistance and local climate.
Do I need blocking between joists?
Add blocking at butt joints, around stairs and where the deck attaches to the house. It transfers load and keeps the joists straight; your plans or inspector may require more.
Assumptions and accuracy
- Dimensions are converted to feet before the calculation; 1 ft = 12 in = 0.3048 m.
- Waste allowances are estimates. Add more for irregular shapes, many cuts and uneven subgrade.
- Bag yields, coverage rates and material densities vary by product. Check the label or ask your supplier.
- Local building codes and site conditions always take precedence over a general-purpose calculator.
- Read our full methodology