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Deck Calculator

Calculate deck boards, joists, and posts for any rectangular deck. Configurable board width, gap, and joist spacing.

Inputs

Result

Deck boards
52
Joists
13
Posts
4
Area
192 ft²
Board
5.5" × 12'

Waste default: 5% — IRC recommends 5% for end cuts and matching grain.

Diagram

Width × Length

Estimates only. Verify with a licensed contractor or supplier before purchasing. Rough Estimator! is not responsible for shortages, overages, or material variances. See our methodology for formulas and sources.

Formula

Boards = ceil(width ÷ (boardW + gap) × ceil(length ÷ boardL))

Related tools & materials

Don't forget

  • Joist hangers
  • Deck screws
  • Post anchors
  • Flashing tape
  • Sealer

Frequently asked questions

Using 5/4 × 6 boards 12 ft long with 1/8" gaps, you need about 26 boards plus joists and posts.

Cite this page

Cosyslabs. (2026). Deck Calculator. Rough Estimator!. https://roughestimator.com/deck-calculator

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