Deck Lumber Calculator
Building a deck requires careful material planning across multiple lumber categories. This calculator estimates the complete structural package: decking boards (with 10% waste for end cuts and defects), floor joists, beams, and 4×4 posts based on your deck dimensions, joist spacing, and deck height off the ground. Decking boards run perpendicular to the joists — the most common layout — and the board count depends on the actual face width of the board, not the nominal size (a 5/4×6 board is 5.5 inches wide). Joists carry the floor load to the beams, and beam count depends on deck width. Posts are spaced in a grid at 8 feet maximum center to center. Always verify joist and beam spans against the AWC span tables or your local building department before purchase.
Buy MaterialsAD
Top Pick5/4×6 Cedar Deck Board — Home Depot~$10.98/board* Affiliate links — we may earn a commission at no cost to you.
Related Calculators
How to Use This Calculator
- 1Enter your measurements in the fields above. Use the units shown next to each field (ft, in, etc.).
- 2Click Calculate to get your material estimate instantly.
- 3Review the highlighted result — it shows the key quantity you need to order.
- 4Use Copy Results to save your estimate, or bookmark the URL — your inputs are encoded in the link.
Pro tip: Always add 10% to your material order to account for waste, cuts, and defects.
Frequently Asked Questions
How many decking boards do I need for a 16×12 deck?
A 16×12 ft deck is 192 sq ft. Using 5/4×6 boards (5.5" wide = 0.458 ft), you need 192 ÷ 0.458 ≈ 419 linear feet of decking, or about 26 boards at 16 ft each — plus 10% waste adds 3 more boards, totaling 29 boards.
What size joists do I need for a deck?
For 16-inch OC spacing, 2×8 joists can span up to 14 feet; 2×10 can span up to 17 feet. At 12-inch OC, 2×8 spans up to 16 feet. Always verify with the AWC Span Table or your local building department.
How much does it cost to build a deck?
Pressure-treated lumber deck materials run $15–$25 per square foot; composite decking runs $30–$60 per square foot in materials. Professional installation adds $20–$40 per square foot in labor. A 12×16 ft deck (192 sq ft) typically costs $3,000–$5,000 for PT lumber DIY build, or $8,000–$20,000 professionally installed with composite decking.
What is the difference between 5/4 decking and 2×6 decking?
5/4×6 decking boards (1" thick actual) are lighter, easier to handle, and the standard choice for most residential decks. 2×6 boards (1.5" thick actual) are stronger and better for heavy loads or wide joist spacing. 5/4 boards can span 16" OC joists; 2×6 boards can span 24" OC, reducing joist count.