2x8 vs 2x10 Deck Joists: Which Should You Use?

Choosing between 2x8 and 2x10 joists usually comes down to one question: how far does the deck project out from the house? The bigger joist buys span, but it also costs more and raises the deck's framing height.

The span difference

In Southern Pine at 16" on-center, a 2x8 spans 11'10" and a 2x10 spans 14'0" — a bit over two extra feet. If your deck projects 12 ft, a 2x8 won't make it and you need the 2x10 (or you tighten the spacing to 12", where the 2x8 reaches 13'1").

Cost and stiffness

• 2x10 lumber costs more per foot and is heavier to handle.
• A deeper joist is stiffer, so even within its allowable span the deck feels more solid.
• Deeper joists raise the framing — check it still tucks under the door threshold.

Let the table decide

Rather than guess, enter your projection and spacing into the calculator. It returns the smallest joist that legally clears your span, so you only pay for the lumber you actually need.