Deck Calculator
Estimate decking boards, joists, posts, and hardware needed for your deck project with cost breakdown.
How to Use This Calculator
Enter your deck's length, width, board width, joist spacing, and local material cost. The calculator estimates board count, joists, posts, and total material cost — useful for planning lumber purchases and budgeting your project.
Formula & Method
Board count = ⌈(deck width ÷ board width in ft) × 1.1⌉ to include 10% waste. Joists = ⌈deck length ÷ spacing in ft⌉ + 1. Posts ≈ ⌈length ÷ 6⌉ × 2 + 2. Material cost = deck area × price per sq ft.
Calculation Example
12 × 16 ft deck, 5.5" boards, 16" joist spacing, $8/sq ft: ~34 boards, 13 joists, 8 posts. Estimated material cost $1,536. Add 10–15% contingency for cuts and defects.
Expert Tips
Buy at least 10% extra boards for end cuts and defects. Composite decking costs 2–3× more than pressure-treated lumber but eliminates staining and annual maintenance. Most jurisdictions require permits for decks over 30 inches above grade — check with your local building department.
Frequently Asked Questions
What size joists should I use?
For residential decks, 2×8 joists span up to 10 ft at 16" spacing. 2×10 joists span up to 14 ft. Always check local building codes.
Do I need a permit?
Most areas require a permit for decks over 30 inches above grade or larger than 200 sq ft. Check with your local building department.