Deck Calculator

Calculate decking boards, joists, posts, and fasteners for your deck project. Works for wood, composite, and PVC decking.

🪵 Enter Your Deck Dimensions

16 in is standard for most decking

Planning your budget?

Read the full Deck Cost Guide 2026

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How to Calculate Deck Materials

Our deck calculator helps you estimate decking boards, joists, posts, and fasteners for your deck building project. Whether using wood, composite, or PVC decking, accurate material estimates help you budget and plan effectively.

Standard Deck Board Sizes

  • 5/4 x 6 Decking: Actual 1 x 5.5 inches - most common
  • 2 x 6 Lumber: Actual 1.5 x 5.5 inches
  • Composite Boards: Typically 1 x 5.5 or 1 x 7.25 inches

Joist Spacing Guidelines

Standard joist spacing is 16 inches on center for most decking materials. Use 12-inch spacing for diagonal patterns or thinner boards. Some heavy-duty composite boards allow 24-inch spacing.

Deck Framing Materials

Always use pressure-treated lumber for structural components (joists, beams, posts) that will be near the ground or exposed to moisture. For the deck surface, choose from pressure-treated wood, cedar, redwood, composite, or PVC decking based on your budget and maintenance preferences.

Frequently asked questions

How many deck boards do I need for a 12x12 deck?⌄
A 12x12 deck (144 sq ft) needs about 24 standard 5.5 inch wide, 12 ft long deck boards including 10% waste. That works out to roughly 26 boards across the 12 ft width before waste, with each board spanning the full 12 ft length.
What joist spacing do I need for composite decking?⌄
Most composite decking requires 16 inch on-center joist spacing for boards installed perpendicular to the joists, and 12 inch spacing for diagonal patterns. Always check the manufacturer span chart, as some heavy-duty composite boards allow 24 inch spacing.
How much does a deck cost per square foot in 2026?⌄
In 2026, a professionally installed deck typically costs $15 to $60 per square foot. Pressure-treated wood sits at the low end ($15-$25), cedar runs $25-$40, and composite or PVC decks run $30-$60 per square foot installed. DIY can cut those numbers roughly in half.
How many screws do I need per deck board?⌄
Use 2 screws at every joist crossing. With 16 inch joist spacing, that works out to roughly 350 screws per 100 square feet of decking, which is the estimate this calculator uses.
Do I need flashing at the ledger board?⌄
Yes. Ledger flashing is required by code in most areas and is one of the most important details on an attached deck. Without it, water gets trapped between the ledger and the house, rotting the rim joist and causing the most common type of deck collapse.

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