Quick answer: Divide the deck width by the board width plus the gap to get the number of rows, multiply by the deck length for total linear feet, add 10% and divide by the board length. A 12 × 16 ft deck with 5.5 inch boards needs 26 rows, or 29 boards of 16 ft including waste.
Deck boards are the most expensive part of most decks, so it pays to count them carefully. Here is the method, a chart for common deck sizes and tips for reducing waste.
Step 1: Count the Rows
Most 5/4×6 and 2×6 boards are 5.5 inches wide. Add the gap between boards, typically ⅛–3/16 inch, to get the width each row takes.
Rows = Deck width (in) ÷ (Board width + Gap), rounded up
For a 12 ft (144 in) wide deck: 144 ÷ 5.625 = 25.6, so 26 rows.
Step 2: Total Linear Feet
Linear feet = Rows × Deck length
26 rows × 16 ft = 416 linear feet of decking.
Step 3: Convert to Boards
Boards = Linear feet × 1.10 ÷ Board length
With 16 ft boards: 416 × 1.1 ÷ 16 = 28.6, so 29 boards. Choosing a board length that matches the deck length avoids butt joints and cuts waste.
Skip the math: enter your deck size, board width, gap and joist spacing to get boards, joists and screws. Open the free Deck Calculator →
Deck Boards Chart
5.5 inch boards, ⅛ inch gaps, boards running the long way, 10% waste:
| Deck size | Rows | Board length | Boards |
|---|---|---|---|
| 10 × 10 ft | 22 | 10 ft | 25 |
| 12 × 12 ft | 26 | 12 ft | 29 |
| 12 × 16 ft | 26 | 16 ft | 29 |
| 12 × 20 ft | 26 | 20 ft | 29 |
| 16 × 20 ft | 35 | 20 ft | 39 |
Joists and Screws
- Joists at 16 in on center: deck length in inches ÷ 16, plus 1. A 16 ft deck needs 13 joists.
- Screws: two per board at every joist. A 12 × 16 deck with 26 rows and 13 joists needs about 676 screws.
- Diagonal layouts and many composite boards need joists at 12 in on center, which adds joists and screws.
Wood vs Composite
Composite and PVC boards have specific gap and joist spacing requirements, and many use hidden fasteners instead of face screws. Always follow the manufacturer’s installation guide to keep the warranty valid.
Planning Tips
- Check local codes and permit requirements; most raised or attached decks need a permit.
- Footings, beams and joist sizes depend on span tables and loads.
- Pour footings with help from our concrete calculator.
- Adding a railing or privacy screen? See how many posts you need.
Frequently Asked Questions
How many deck boards do I need for a 12×12 deck?
With 5.5 inch boards and ⅛ inch gaps, a 12 × 12 deck needs 26 rows, or 29 boards of 12 ft with 10% waste.
What gap should I leave between deck boards?
About ⅛ to 3/16 inch for dry wood and most composites. Wet pressure-treated boards are often installed tight because they shrink as they dry.
How many linear feet of decking per square foot?
With 5.5 inch boards and a ⅛ inch gap, you need about 2.13 linear feet of board for each square foot of deck.
Related Guides
- How Many Squares Is My Roof? How to Measure a Roof from the Ground
- Roof Pitch Explained: How to Measure It and Convert to Degrees
- How Many Fence Posts Do I Need? (With Corners and Gates)
Try the free Deck Calculator or browse all home improvement calculators.