Lumber Spans

Formula and source

Allowable simple-beam span: deflection-limited L = sqrt(48 × E × I × Δ_allow / (5 × w × n)); strength-limited from M_allow = Fb × S. F_b and E from AWC NDS-2018 design values; deflection limit L/360 (live) or L/240 (total) per IRC §R301.7.

AWC NDS-2018 (National Design Specification for Wood Construction). IRC 2021 (International Residential Code). §R301.7, R502.3, R802.4.

Audience

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Related tools

• Beam Loading
• Joist Mid-Span Deflection
• Rafter Length
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Posture

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