Wood Beam Span Calculator
Floor Joist Span
Calculate maximum span for floor joists at 40 PSF live load
Header / Beam Sizing
Determine beam size needed for a given span and load
Formula
Max Moment = wL^2/8 | Required S = M / Fb | Deflection limit = L/360
Frequently Asked Questions
How far can a 2x10 span as a floor joist?
A #2 SPF 2x10 floor joist at 16" O.C. spacing can span approximately 15.5 feet for a standard 40 PSF live load floor. Douglas Fir #2 can span about 17 feet. Closer spacing (12" O.C.) increases the span by 1-2 feet.
How do I size a wood beam for a given span?
Calculate the total load per linear foot (tributary width x PSF). Then find the maximum bending moment (M = wL^2/8). Divide the moment by the allowable bending stress (Fb) to get the required section modulus (S). Select a beam with S greater than or equal to the required value.
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