How Much Lumber Do I Need for a Deck?
Enter your deck dimensions to estimate decking boards, joists, posts, and fasteners needed for your build.
How to Calculate Deck Lumber
Calculate deck area (length × width), then divide by the board width to get the number of rows needed. For 2×6 decking (actual width 5.5") on a 12-foot wide deck: 12 ft × 12 in/ft ÷ 5.5" = 26 rows of boards. Add 10% for waste from end cuts and any defective boards you'll encounter.
For joists at 16" on center: divide the deck length by the spacing and add 1 for the end joist. A 16-foot long deck needs (16 ÷ 1.33) + 1 = 13 joists. This is the structural framing that runs perpendicular to the decking boards.
Deck Lumber: Pressure-Treated vs. Composite
Pressure-treated lumber is the standard choice for deck framing (posts, beams, joists) and is often used for decking boards as well. It's the most affordable option — a basic 12×16 deck can be framed and decked in PT lumber for $2,000–$4,000 in materials. Requires annual sealing or staining to prevent weathering, and boards need to dry out for 3–6 months after installation before staining.
Composite decking (Trex, TimberTech, Fiberon) uses the same pressure-treated framing but replaces wood decking boards with a composite material. Composite costs $4–$12 per linear foot vs. $2–$4 for PT wood, but requires no staining, sealing, or splinter-proofing. Over 20 years, the maintenance savings often justify the higher upfront cost. Most composite products carry 25–30 year warranties.
Best practice: use pressure-treated lumber for all framing (posts, beams, joists) regardless of your decking choice. The framing is in contact with the ground or close to moisture and must be rated for ground contact (look for UC4B or UC4C rating).
Do You Need a Permit for a Deck?
Most jurisdictions require a building permit for attached decks above a certain height (commonly 12–18 inches above grade) or over a certain size (often 200 sq ft). Permit requirements vary significantly by municipality. Always check with your local building department before starting — unpermitted decks can cause problems at resale and may need to be removed.
Detached, ground-level platforms under 200 sq ft often don't require permits, but setback requirements from property lines still apply. Your local building department can tell you the exact rules for your area in about 5 minutes.