Deck Board Calculator Formula
Understand the math behind the deck board calculator. Each variable explained with a worked example.
Formulas Used
Deck Area
deck_area = deck_length * deck_widthBoards Across Width
boards_across = ceil(deck_width / board_coverage_width)Linear Feet of Boards
linear_feet = ceil(deck_width / board_coverage_width) * deck_lengthBoards Needed
boards_needed = ceil(ceil(deck_width / board_coverage_width) * deck_length / board_length * (1 + waste_percent / 100))Variables
| Variable | Description | Default |
|---|---|---|
deck_length | Deck Length(feet) | 16 |
deck_width | Deck Width(feet) | 12 |
board_width | Board Width (nominal)(inches) | 5.5 |
gap | Gap Between Boards(inches) | 0.125 |
board_length | Board Length(feet) | 16 |
waste_percent | Waste Factor(%) | 10 |
board_coverage_width | Derived value= (board_width + gap) / 12 | calculated |
How It Works
How to Calculate Deck Boards
Formula
Boards Across = Deck Width / (Board Width + Gap)
Total Boards = Boards Across × Deck Length / Board Length × (1 + Waste)
A nominal 2×6 deck board is actually 5.5 inches wide. Include a 1/8-inch gap between boards for drainage and expansion. Board lengths come in 8, 10, 12, 14, 16, and 20 ft.
Worked Example
A 16 ft by 12 ft deck with 5.5-inch (2×6) boards, 1/8-inch gaps, 16 ft board length, 10% waste.
- 01Board coverage width = (5.5 + 0.125) / 12 = 0.469 ft
- 02Boards across = 12 / 0.469 = 25.6 → 26 boards
- 03Linear feet = 26 × 16 = 416 lin ft
- 04Boards at 16 ft = 416 / 16 = 26 boards
- 05With 10% waste = 26 × 1.10 = 28.6 → 29 boards
Frequently Asked Questions
What is the actual size of a 2×6 deck board?
A nominal 2×6 is actually 1.5 inches thick by 5.5 inches wide. This is important for calculating coverage.
How much gap should I leave between deck boards?
Leave 1/8 inch between wood boards for drainage and expansion. Composite decking may require different spacing per the manufacturer.
Should I use screws or nails for deck boards?
Use coated deck screws (2.5 or 3 inch) for the best hold. Use 2 screws per joist per board. Hidden fastener systems are another option for a clean look.
Learn More
Guide
Understanding Lumber Dimensions: Nominal vs. Actual Sizes
Learn the difference between nominal and actual lumber dimensions. Covers common framing sizes, board feet calculations, hardwood grading, and how to choose the right lumber for your project.
Ready to run the numbers?
Open Deck Board Calculator