Deck Calculator
Estimate deck boards, square footage and joist count for any deck project.
Square Footage
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Number of Deck Boards
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Total Linear Feet
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Number of Joists (16" OC)
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Estimated Posts
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How the Deck Calculator Works
This deck calculator estimates materials for a rectangular deck. Square footage is simply length times width. The number of boards is calculated by dividing the deck width by the effective board width (actual board width plus gap), rounded up. Total linear footage equals the number of boards multiplied by the board length. Joists are placed 16 inches on center across the deck length, plus one end joist. Posts are estimated at one per 8 linear feet of perimeter, which is a common spacing for beam support. These are planning estimates — always consult local building codes and a structural engineer for permitted decks over 30 inches off the ground.
Frequently Asked Questions
How many deck boards do I need for a 12×16 deck?
A 12×16 deck (192 sq ft) using 5.5-inch boards at ¼-inch gap needs approximately 26–28 boards at 16-ft length.
What is standard deck board spacing?
1/8 to 1/4 inch gap between boards allows for drainage and seasonal wood movement.
How many joists do I need for a deck?
Place joists 16 inches on center. For a 16-ft deck, that's approximately 13 joists.
What size deck can I build without a permit?
Most jurisdictions allow decks under 200 sq ft, under 30 inches off the ground, and not attached to the house without a permit. Always verify locally.