Engineering

Deck Calculator | Boards, Joists, Posts & Material Estimator

Calculate deck boards, joists, posts, concrete footings, rim boards, and hardware for any wood or composite deck. Enter dimensions, board width, and joist spacing — with diagonal board options and a complete material summary with optional cost estimate.

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Deck Dimensions

Length (ft)

Width (ft)

Decking Material

Board Width (actual inches)

Joist Spacing

Deck Height

Waste Factor

Diagonal boards

Include railing

Deck Material Comparison

Material	Cost/sq ft	Lifespan	Maintenance
Pressure-Treated Wood	$2–4	15–25 yrs	Annual staining/sealing
Cedar / Redwood	$4–7	15–30 yrs	Biennial sealing
Composite (Trex, etc.)	$6–12	25–30 yrs	Low — wash yearly
Ipe (Hardwood)	$10–20	40–75 yrs	Annual oiling

Joist Spacing and Span

Joist spacing of 16 inches on-center is standard for most deck boards. Composite and PVC decking often requires 12-inch spacing due to deflection limits. For 5/4×6 pressure-treated decking, maximum unsupported span is 16 inches; for 2×6 solid lumber, up to 24 inches.

Permits and Building Codes

Most jurisdictions require a building permit for decks over 200 square feet or those attached to the house. Railing height must be at least 36 inches for decks under 30 inches above grade, and 42 inches for higher decks. Balusters must be spaced so a 4-inch sphere cannot pass through.

Pro Tip: For composite decking installed diagonally, add 15% to your board count for the extra cuts. Diagonal patterns also require joists spaced 12 inches on-center instead of the standard 16 inches.

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