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Deck Calculator
Project Calculators

Deck Calculator

Calculate deck boards, joists, screws, and material cost for your deck.

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How to calculate deck materials

  1. Enter your deck's length and width in feet. These are the outer frame dimensions, not the post layout.

  2. Enter the deck board width and gap size. Standard 5/4×6 decking is 5.5 inches wide; most builders leave a 1/4-inch gap for drainage.

  3. Set joist spacing — 16 inches on center is standard for most decking; 12 inches for composite.

  4. Add a price per board and price per joist to get a full material cost breakdown.

Common uses

  • Planning a new backyard deck build from scratch
  • Estimating replacement boards for a deck repair
  • Getting a materials list before pulling a permit

Frequently asked questions

How many deck boards do I need for a 12×16 deck?
A 12×16 deck using standard 5.5-inch boards with 1/4-inch gaps needs about 26 boards, running across the 12-foot width. Add 10–15% for waste and end cuts.
What's the standard joist spacing for a wood deck?
Sixteen inches on center works for most solid wood decking. Composite decking often requires 12-inch spacing — check your manufacturer's guidelines.
How much does it cost to build a deck per square foot?
Materials alone typically run $15–30 per sq ft for pressure-treated wood, and $30–60 for composite. Labor adds another $15–35 per sq ft if you hire a contractor.

Not sure whether to DIY this project?

Read our project-by-project guide on when to hire a contractor vs. do it yourself.

Read the guide →

About this calculator

Enter your deck dimensions, board width, gap size, and joist spacing to get exact material counts and estimated cost. Supports 5/4 decking and standard lumber.

All results are estimates. Verify quantities with your local supplier and confirm measurements before purchasing materials. Requirements vary by region and project type.

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