BuildCalc
BuildCalc
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Deck Calculator
Deck Calculator
Project Calculators

Deck Calculator

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

DIY difficulty

HardTypical time: 2–4 weekends
  • ›Most areas require a building permit — pull it before starting
  • ›Ledger attachment to the house must be done correctly to prevent collapse
  • ›Footings must go below the frost line in cold climates

Must-have tools

Post hole digger or augerLevel and string lineCircular sawDrill + impact driver

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 many screws do I need per deck board?
Use 2 screws per joist crossing per board — so at 16" O.C. joist spacing, each 16-foot board gets roughly 24 screws. The calculator estimates this automatically.
What is the best wood for a deck?
Pressure-treated pine is the most economical and widely available. Cedar and redwood are naturally rot-resistant and look better but cost more. Composite decking has the highest upfront cost but lowest long-term maintenance.

Common mistakes to avoid

  • ✕Not pulling a permit first — most US jurisdictions require a permit for decks over 30 inches above grade.
  • ✕Undersizing ledger lag screws — the ledger connection is the most critical structural joint. IRC tables specify size and spacing.
  • ✕Wrong joist spacing for composite decking — many composite products require 12" OC instead of standard 16" OC, nearly doubling joist count.
  • ✕Setting footings above the frost line — in cold climates, frost heave will push surface-set posts out of the ground within seasons.

Calculators you might also need

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Find the minimum joist size for your span, species, and spacing. Based on IRC deck joist span tables.
Concrete Calculator
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Fence Calculator
Calculate fence posts, pickets, rails, and total material cost.

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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