Wood Beam Span Calculator

Estimate max simple-beam span from allowable stress.

Max span 10

Max span 120

Formula: L = √(96·Fb·S ÷ w)

Step-by-step with your numbers:

1. Values used:

2. Allowable bending stress (Fb) = 1,200 psi

3. Section modulus (S) = 15 in³

4. Uniform load = 120 lb/ft

6. Max span = 10

7. Max span = 120

Did we solve your problem today?

Estimate the safe span of a simply-supported wooden beam under a uniform load. Verify with span tables / an engineer.

The math behind it

Based on bending: max span L = √(96 × allowable stress × section modulus ÷ uniform load), from M = wL²/8 = Fb·S.

Fb 1200 psi, S 15 in³, 120 lb/ft → ~10 ft.

This isn't final sizing?

Only bending is checked here — shear, deflection and connection capacity also matter.