Deck Joist Spacing (12, 16 or 24 Inches?)
Part of Decks, Fences & Roofing
Quick answer
Standard deck joist spacing is 16 inches on center. Drop to 12 inches for a stiffer deck, for diagonal decking, or when composite boards require it; 24 inches is only allowed with decking specifically rated for that span. 'On center' means measured from the center of one joist to the center of the next.
Joist spacing controls how stiff and bouncy a deck feels and which decking it can carry. Closer joists mean a stronger surface and less deflection, at the cost of more lumber. The decking material's span rating is what ultimately sets the maximum.
Spacing by decking type
| Decking | Perpendicular | Diagonal (45°) |
|---|---|---|
| 5/4 wood deck board | 16 in o.c. | 12 in o.c. |
| 2x wood (5.5") | 16–24 in o.c. | 16 in o.c. |
| Most composite | 16 in o.c. | 12 in o.c. |
| Some premium composite | Up to 24 in o.c. | 16 in o.c. |
What 'on center' means
- Measure from the center of one joist to the center of the next, not the gap between them.
- At 16 in o.c., joists = deck length (in) ÷ 16, plus one closing joist at the end.
- Always follow the decking maker's published span — it overrides rules of thumb and protects the warranty.
- Joist size and the beam/footing spacing depend on the span and load; check a span table or your local code.
The deck calculator counts joists at 12, 16 or 24 inch spacing so you can compare lumber needs for each.
FAQs
Can I put deck joists 24 inches apart?
Only if your decking is rated for a 24-inch span — many composites and thinner boards are not, and will feel bouncy or sag. Wood 2x decking can sometimes span 24 inches, but 16 inches on center is the safe, standard choice for most decks.
Why use 12-inch joist spacing?
Use 12 inches on center for diagonal or herringbone decking (the boards span farther between joists at an angle), for a noticeably stiffer feel, or whenever the decking manufacturer requires it for their warranty.