How far can a 3×6, 3×8, 3×10 and 3×12 beam span without support depends on various factors, including the grade and type of species of wood or material used, the load it will bear, design, construction requirement, and local building codes and regulation.

There are many species of wood/ timber or dimensional lumber used in US, UK & cold region country for house construction as wooden frame structure. It is used as floor joist, floor beam ceiling joist, pitch roof rafter, flat roof rafter, purlin and Binder.

There are different size of beam like 3×6, 3×8, 3×10 and 3×12 made of different species of wood Southern yellow pine, Redwood, Hem-Fir, SPF, & Douglas-Fir with grade-1 & grade-2. The SYP is strongest species of wood that can span more distance compared to other species of wood. Grade-1 lumber have higher strength than other grade Lumber due to fewer knots.

The load consist of live load and dead load measured in pounds per linear foot (PLF). Total load may be 125 plf (100 plf of live load + 25 plf of dead load), 250 plf (200 plf of live load + 50 plf of dead load), or may be 375 plf (300 plf of live load + 75 plf of dead load). Higher the load-shorter the beam span, while lighter load-longer the beam span.

**How far can a 3×6, 3×8, 3×10 and 3×12 beam span without support**

In general, a 3×6 floor beam can allow to span from 8 to 9 feet without support, while a 3×8 floor beam can allow to span from 10 to 11 feet. Likewise, a 3×10 floor beam can allow to span from 12 to 14 feet, while a 3×12 floor beam can allow to span from 14 to 16 feet without support.

**How far can a 3×6 beam span without support**

Typically a #2-grade Douglas-Fir 3×6 floor beam can allow to span a maximum distance of 8 feet and 10 inches without support with a total load of 125 PLF (100 plf of live load + 25 plf of dead load) with a deflection of limit L/360.

**How far can a 3×8 beam span without support**

Typically a #2-grade Douglas-Fir 3×8 floor beam can allow to span a maximum distance of 11 feet and 3 inches without support with a total load of 125 PLF (100 plf of live load + 25 plf of dead load) with a deflection of limit L/360.

**How far can a 3×10 beam span without support**

Typically a #2-grade Douglas-Fir 3×10 floor beam can allow to span a maximum distance of 13 feet and 9 inches without support with a total load of 125 PLF (100 plf of live load + 25 plf of dead load) with a deflection of limit L/360.

**How far can a 3×12 beam span without support**

Typically a #2-grade Douglas-Fir 3×12 floor beam can allow to span a maximum distance of 15 feet and 11 inches without support with a total load of 125 PLF (100 plf of live load + 25 plf of dead load) with a deflection of limit L/360.

**Conclusions:-**

In general, the maximum span of a 3×6 floor beam should be 9 feet, while the maximum span of a 3×8 floor beam ought to be 11 feet. Likewise, the maximum span of a 3×10 floor beam need to be 14 feet, while the maximum span of a 3×12 floor beam got to be 16 feet.