Wood Beam Span Conversion Chart
| Beam Size (inches) | Maximum Span (feet) | Conversion Equation |
|---|---|---|
| 2×4 | 5-7 | 1 foot = 12 inches |
| 2×6 | 8-10 | 1 foot = 12 inches |
| 2×8 | 10-12 | 1 foot = 12 inches |
| 2×10 | 13-16 | 1 foot = 12 inches |
| 2×12 | 16-20 | 1 foot = 12 inches |
| 4×6 | 10-12 | 1 foot = 12 inches |
| 4×8 | 13-16 | 1 foot = 12 inches |
| 4×10 | 16-20 | 1 foot = 12 inches |
| 4×12 | 20-24 | 1 foot = 12 inches |
| 6×6 | 12-15 | 1 foot = 12 inches |
| 6×8 | 15-18 | 1 foot = 12 inches |
| 6×10 | 18-22 | 1 foot = 12 inches |
| 6×12 | 22-26 | 1 foot = 12 inches |
Note: Actual spans may vary based on wood species, grade, and load requirements.
Wood Beam Span Formula
The formula for calculating wood beam span is complex and depends on various factors. A simplified version is:
L = (384 x E x I) / (5 x w x d^4)Where:
- L = Maximum span length (inches)
- E = Modulus of elasticity of wood (psi)
- I = Moment of inertia (inches^4)
- w = Uniform load (pounds per linear inch)
- d = Deflection limit (typically span/360)
For a 2×8 Douglas Fir beam with E = 1,700,000 psi, I = 47.63 in^4, w = 40 lb/ft (3.33 lb/in), and d = 0.4 inches:
L = (384 x 1,700,000 x 47.63) / (5 x 3.33 x 0.4^4) = 140.8 inches (11.73 feet)How long can a wooden beam span?
The span of a wooden beam depends on several factors:
Beam size: Larger beams can span greater distances.
Wood species: Stronger woods like Douglas Fir allow longer spans than softer woods.
Load requirements: Heavier loads reduce maximum span lengths.
Support conditions: Beams with multiple supports can span further than those with only end supports.
Deflection limits: Stricter deflection requirements reduce allowable spans.
For example, a 2×10 Southern Pine beam (No. 2 grade) supporting a typical residential floor load might span up to 16 feet when spaced 16 inches apart. However, the same beam used as a header over a wide opening might only span 8-10 feet due to increased load concentration.