Wood Beam Span Calculator
Calculate wood beam capacity, deflection, bending and shear stress with NDS standards
Wood Beam Analysis
Wood Species & Grade
Beam Dimensions
Actual width (not nominal)
Actual height (not nominal)
Load & Span
Unbraced length of beam
Distributed load along beam
Deflection Criteria
Building code deflection requirements
Structural Analysis Results
⚠️ Structural Engineering Warning
• This calculator provides estimates based on simplified NDS calculations
• Always consult a licensed structural engineer for load-bearing applications
• Consider local building codes, environmental conditions, and safety factors
• Account for connection details, lateral support, and dynamic loads
• Professional structural analysis required for critical applications
• Verify lumber grade, species, and moisture content before use
Example: 2×10 Douglas Fir Beam Analysis
Beam Specifications
Wood Species: Douglas Fir-Larch, Select Structural
Beam Size: 2×10 (actual: 1.5" × 9.25")
Span: 8 feet (96 inches)
Load: 240 lbf/ft (20 lbf/in)
Deflection Limit: L/240
Calculated Results
• Section Modulus (S) = 1.5 × 9.25² / 6 = 21.39 in³
• Moment of Inertia (I) = 1.5 × 9.25³ / 12 = 98.93 in⁴
• Deflection = 5 × 20 × 96⁴ / (384 × 1,900,000 × 98.93) = 0.109"
• Max Deflection = 96/240 = 0.4" ✅ PASS
• Bending Stress = (20 × 96² / 8) / 21.39 = 1,074 psi
• Allowable Bending = 1,500 × 0.85 = 1,275 psi ✅ PASS
Result: Beam passes all structural checks
Common Wood Species
Douglas Fir-Larch
E: 1.9 million psi, Fb: 1500 psi
Southern Pine
E: 1.8 million psi, Fb: 1500 psi
Hem-Fir
E: 1.6 million psi, Fb: 1400 psi
Spruce-Pine-Fir
E: 1.5 million psi, Fb: 1200 psi
Lumber Grades
Select Structural
Highest grade, minimal defects
No. 1 & Better
High quality, structural use
No. 2
Most common structural grade
Construction
Light framing applications
Deflection Limits
Understanding Wood Beam Structural Analysis
Deflection Analysis
Beam deflection is calculated using the formula δ = 5×w×L⁴/(384×E×I), where the deflection must not exceed the allowable limit (typically L/240 for combined dead and live loads per IBC).
Bending Stress Check
The actual bending stress (fb = M/S) must not exceed the adjusted allowable bending stress. The moment is calculated as M = w×L²/8 for uniformly distributed loads.
Shear Stress Analysis
Shear stress (fv = V/A) is calculated from the maximum shear force (V = w×L/2) and must not exceed the adjusted allowable shear stress for the wood species and grade.
NDS Adjustment Factors
Duration Factor (CD)
Adjusts for load duration: 0.9 (permanent), 1.0 (10 years), 1.15 (2 months), 1.25 (7 days), 1.6 (10 minutes), 2.0 (impact)
Wet Service Factor (CM)
Accounts for moisture content above 19%: typically 0.85 for bending, 0.97 for shear
Size Factor (CF)
Adjusts for lumber size effects on strength properties
Note: This calculator uses simplified adjustment factors. Professional analysis should consider all applicable factors per NDS.