Size finder
What size do I need?
Enter the clear span you have to cover, then the tool returns the smallest nominal size that reaches it for your species, grade, and spacing — reverse-looked-up from the published tables.
Smallest size that reaches your span
2x8spans 12′-9″
A 2x8 Douglas Fir-Larch at 16″ o.c. covers your 12′-0″ span (published max 12′-9″). Smaller sizes in this table fall short.
Source: International Residential Code (IRC), 2018 — Table R502.3.1(2) — Floor Joist Spans, 40 psf Live Load (International Code Council).