Common Decking Board Sizes
| Nominal | Actual Width | Best For |
|---|---|---|
| 5/4×6 | 5.5" | Residential decks — most popular choice |
| 2×6 | 5.5" | Stronger span, better for wide joist spacing |
| 2×4 | 3.5" | Smaller decks, tighter look |
| 2×8 | 7.25" | Wide plank look, premium decks |
Joist Spacing for Decking
Standard treated lumber decking (5/4×6 or 2×6) spans up to 16 inches OC safely. For composite or PVC decking, check the manufacturer specs — many require 12-inch spacing, especially for diagonal installations. Always double-check joist span tables for your specific load. This free tool lets you plug in your board size and deck dimensions to get an instant board count.
Frequently Asked Questions
How many deck boards do I need for a 12×16 deck?+
A 12×16 deck is 192 sq ft. Using 5/4×6 boards (5.5 inch actual width) with ¼-inch gaps, you need approximately 38 boards at 16 feet long, or 42 boards with 10% waste. The exact count depends on board length and run direction.
What is the best wood for a deck?+
Pressure-treated pine is the most popular choice for its affordability and durability ($2–$4/linear ft). Cedar and redwood are naturally rot-resistant and look beautiful ($4–$8/lf). Composite decking (Trex, TimberTech) costs more upfront ($6–$12/lf) but requires almost no maintenance.
How wide should gaps be between deck boards?+
Leave ¼ to ⅛ inch between boards for drainage and expansion. Green or wet pressure-treated lumber will shrink as it dries, so butting boards tightly often results in proper gaps once dry. Use a 16d nail as a spacer for consistent gaps.
What joist spacing do I need under decking?+
Standard 5/4×6 decking spans 16 inches OC safely for straight installation. For diagonal decking (45°), reduce joist spacing to 12 inches OC. Composite and PVC decking has its own span requirements — always check the manufacturer specs.