Deck Joist Spacing: 12 vs 16 vs 24 Inches

Joist spacing — the on-center distance between joists — is one of the biggest levers you have on a deck. It changes how far the joists can span, what decking you can run, and how solid the deck feels underfoot.

16" on-center is the default

Most decks frame at 16" o.c. It balances span, lumber cost and stiffness, and it suits standard decking laid perpendicular to the joists. A 2x8 Southern Pine joist spans 11'10" at 16".

When to go to 12"

• You're laying decking on a diagonal (the boards span a longer distance between joists).
• You want a stiffer, bounce-free deck.
• You need a bit more span out of the joist size you have on hand.

When 24" works

24" o.c. uses less lumber and is allowed by the tables, but it shortens the span, can feel springy, and many composite deck boards require 16" or even 12" spacing — always check the decking manufacturer's instructions. Run your numbers through the calculator at each spacing to see the trade-off.