Deck Board Calculator — How Many Deck Boards Do I Need?
Calculate the exact number of deck boards, joists, joist hangers, and screws needed for your deck project. Supports standard and diagonal laying patterns.
How to Use This Calculator
- Enter your deck length and width in feet
- Choose the board width and the length you plan to purchase
- Select the gap between boards (1/8" is standard)
- Choose your laying pattern — diagonal adds 15% extra material
- Adjust the waste factor and click "Calculate Deck Materials"
How the Calculation Works
effective_board_width = board_width_in + gap_in
boards_needed = ceil(deck_width_in / effective_board_width)
// Diagonal: multiply boards_needed by 1.15
boards_to_buy = ceil((boards_needed × deck_length_ft) / board_length_ft) × (1 + waste)
joists_16oc = ceil(deck_length_ft / 1.333) + 1
deck_screws_lbs = (deck_length × deck_width) × 0.075 The calculator determines how many board runs span the deck width, accounting for the gap between boards. Board count is converted to purchasable lengths. Joists are calculated at 16" on-center spacing (standard residential framing), plus one extra for the rim joist. Screw quantity is based on approximately 0.075 lbs of screws per square foot.
Variables:
- effective_board_width: Actual board width plus the gap between boards
- boards_needed: Number of board runs to cover the deck width
- boards_to_buy: Total boards to purchase at the chosen length
- joists_16oc: Number of 2×8 or 2×10 joists at 16" on-center
- deck_screws_lbs: Approximate weight of deck screws needed
Pro Tips
- Leave a 1/8" gap between boards for drainage and expansion — wet wood swells, dry wood shrinks
- Use stainless steel or hot-dipped galvanized screws to prevent rust staining on your deck
- Diagonal patterns use 15% more material due to angled cuts at the perimeter
- For spans over 8ft, upgrade to 2×10 joists to prevent sagging and meet code requirements
- Apply a deck sealer or stain within 6 months of installation to protect against moisture
Recommended Products
Frequently Asked Questions
How many deck boards do I need for a 12x16 deck?
For a 12×16 deck (192 sq ft) using standard 2×6 boards (5.5" wide) with 1/8" gaps, you need approximately 27 board runs. At 16ft board lengths, that is about 27 boards plus 10% waste = 30 boards.
What size screws should I use for deck boards?
Use 2.5" (6d) or 3" (10d) decking screws. For 2×6 boards, 3" screws penetrate deep enough into joists. Always use stainless steel, hot-dipped galvanized, or coated screws rated for exterior use.
What is the standard gap between deck boards?
A 1/8" gap is standard and allows for drainage and small expansion. Boards will swell slightly when wet, so installing when the wood is dry with a 1/8" gap typically results in a tight but functional gap when wet.
How far apart should deck joists be?
16" on-center is standard for 2×6 decking (5/4 decking requires 12–16" OC). 24" OC spacing requires 2×6 decking at minimum. Always check local building codes for your specific application.
How much extra should I order for a diagonal deck pattern?
Add 15% extra for a diagonal (45°) pattern due to waste from angled cuts at the perimeter. This calculator automatically adjusts the quantity when you select a diagonal pattern.