Deck Calculator
Calculate deck materials including decking boards, joists, posts, and concrete. Estimate costs for wood, composite, and PVC decking projects.
Deck Dimensions
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ft
Decking Details
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ft
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Last updated: January 2026
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Frequently Asked Questions
How do I calculate how many deck boards I need?
Divide your deck's square footage by the coverage area of one board. For a 5.5-inch wide × 12-foot board, coverage is about 5.5 square feet (accounting for 1/8" gaps between boards). For a 300 sq ft deck using 5.5" × 12' boards: 300 ÷ 5.5 ≈ 55 boards. Add 10-15% for waste, cuts, and defects, so order 60-65 boards. For angled or complex designs, add 20% waste factor.
What is the best decking material for durability and value?
Pressure-treated pine costs $2-4/sq ft and lasts 15-20 years with proper maintenance. Cedar costs $4-8/sq ft, resists rot naturally, and lasts 15-25 years. Composite ($6-12/sq ft) lasts 25-30+ years with minimal maintenance but can get hot in sun. Hardwoods like Ipe ($15-25/sq ft) last 40+ years but are expensive. For most homeowners, composite offers the best long-term value despite higher upfront cost.
What joist spacing should I use for my deck?
Standard joist spacing is 16 inches on-center for most residential decks using 2×6 or thicker decking. Use 12-inch spacing for: composite decking (check manufacturer specs), diagonal board patterns, or heavy-traffic areas. Use 24-inch spacing only for 2×6 or thicker solid wood decking in low-traffic areas. Always check local building codes and the decking manufacturer's requirements for specific spacing.
When do I need a permit to build a deck?
In most US jurisdictions, you need a permit if your deck is: more than 200 square feet, more than 30 inches above grade, attached to the house, or includes electrical/plumbing. Permits typically cost $100-500 and require inspections. Building without a required permit can result in fines, forced removal, or problems selling your home. Always check with your local building department before starting construction.
How much concrete do I need for deck post footings?
Each footing typically requires 1-3 bags of 60lb concrete depending on depth and diameter. Standard footings are 12 inches diameter × 36-48 inches deep (below frost line). A 12" × 36" footing needs about 2.5 bags. For a typical 300 sq ft deck with 9 footings, plan for 25-30 bags. Check local frost depth requirements—footings must extend below the frost line to prevent heaving, which ranges from 12 inches in the South to 48+ inches in northern states.