🪵 Wood Beam Span Calculator
Calculate beam size, span capacity, and deflection for wood beams
Standard: 10-15 psf (flooring, subfloor, beam weight)
How to Use This Calculator
Enter Span Length
Input the span length in feet - the distance the beam must span between supports (e.g., 12 feet for a 12-foot span).
Specify Beam Dimensions
Select beam width and depth in inches. Common sizes include 2×8, 2×10, 2×12, or larger beams like 6×8, 8×8. Width is the horizontal dimension, depth is the vertical dimension.
Set Load Requirements
Select live load (standard is 40 psf for residential floors) and dead load (standard is 10-15 psf). Live load is the weight of people and furniture; dead load is the weight of permanent materials.
Calculate and Review
Click "Calculate Beam Span" to see bending stress, deflection, and safety factor. The beam is adequate if safety factor ≥ 100% and deflection is within L/360 limit. For critical structures, consult a structural engineer.
Formula
Moment of Inertia (I) = b × d³ / 12
Section Modulus (S) = b × d² / 6
Bending Moment (M) = (w × L²) / 8 (uniform load)
Bending Stress (fb) = M / S
Deflection (δ) = 5wL⁴ / (384EI)
Where: b = width, d = depth, L = span, w = load per foot, E = modulus of elasticity
Example 1: Standard Floor Beam (12 ft span, 2×10, #2 grade, 40 psf live + 10 psf dead)
Step 1: Beam dimensions: 5.5" × 9.25"
Step 2: Calculate I: (5.5 × 9.25³) / 12 = 362 in⁴
Step 3: Calculate S: (5.5 × 9.25²) / 6 = 78.3 in³
Step 4: Total load: 40 + 10 = 50 psf
Step 5: Line load: 50 × (5.5/12) = 22.9 lbs/ft
Step 6: Bending moment: (22.9 × 12²) / 8 = 412 ft-lbs
Step 7: Bending stress: (412 × 12) / 78.3 = 631 psi (allowable: 900 psi)
Step 8: Safety factor: (900 / 631) × 100 = 143% ✓ Adequate
Example 2: Larger Span (16 ft span, 2×12, #2 grade, 40 psf live + 10 psf dead)
Step 1: Beam dimensions: 5.5" × 11.25"
Step 2: Calculate I: (5.5 × 11.25³) / 12 = 651 in⁴
Step 3: Calculate S: (5.5 × 11.25²) / 6 = 116 in³
Step 4: Total load: 50 psf
Step 5: Line load: 50 × (5.5/12) = 22.9 lbs/ft
Step 6: Bending moment: (22.9 × 16²) / 8 = 733 ft-lbs
Step 7: Bending stress: (733 × 12) / 116 = 758 psi (allowable: 900 psi)
Step 8: Safety factor: 119% ✓ Adequate
About Wood Beam Span Calculator
The Wood Beam Span Calculator is an essential tool for contractors, carpenters, engineers, and DIY enthusiasts who need to determine if a wood beam is adequate for a given span and load, or calculate the required beam size for a project. This calculator provides simplified engineering estimates for bending stress, deflection, and safety factors based on beam dimensions, span length, load requirements, and wood grade.
When to Use This Calculator
- Floor Framing: Calculate beam size needed for floor joist support and load-bearing walls
- Ceiling Beams: Determine beam size for ceiling beam installations and structural support
- Deck Construction: Calculate beam size for deck support beams and framing
- Structural Planning: Estimate beam requirements before ordering materials or starting construction
- Remodeling Projects: Verify existing beams are adequate for new loads or renovations
Why Use Our Calculator?
- ✅ Bending Stress Analysis: Calculates actual vs. allowable bending stress based on wood grade
- ✅ Deflection Calculation: Determines beam deflection and compares to L/360 limit
- ✅ Safety Factor: Shows safety margin to help ensure adequate beam capacity
- ✅ Multiple Wood Grades: Supports different wood grades (#3, #2, #1, Select Structural) with appropriate allowable stresses
- ✅ Standard Loads: Includes common live load values (30-60 psf) for different applications
- ✅ Time Savings: Instant calculations eliminate manual engineering calculations
Common Applications
Floor Framing: Contractors and carpenters planning floor framing use this calculator to determine if beams are adequate for supporting floor joists. Standard residential floors use 40 psf live load with 10 psf dead load, and beams must meet both stress and deflection requirements.
Deck Construction: DIY enthusiasts and contractors planning deck construction use this tool to verify beam sizes for deck support. Deck beams typically use 2×10 or 2×12 beams depending on span and load requirements.
Remodeling Projects: Homeowners and contractors planning remodeling projects use this calculator to verify existing beams are adequate for new loads or determine required beam sizes for new openings.
Tips for Best Results
- Beam Orientation: Width is horizontal dimension, depth is vertical - depth has much more impact on strength
- Wood Grade: Higher grades (#1, Select Structural) have higher allowable stresses but cost more
- Live Load: Standard residential floors use 40 psf; bedrooms use 30 psf; storage areas use 60 psf
- Dead Load: Standard dead load is 10-15 psf (includes flooring, subfloor, and beam weight)
- Deflection Limits: Standard deflection limit is L/360 (span/360) for floors to prevent bounce
- Consult Engineer: For critical structures, always consult a licensed structural engineer
Frequently Asked Questions
What size beam do I need for a 12-foot span?
For a 12-foot span supporting residential floor loads (40 psf live + 10 psf dead), a 2×10 beam (#2 grade) is typically adequate. The calculator shows bending stress, deflection, and safety factor. For critical structures, consult a structural engineer.
What is the difference between beam width and depth?
Beam width is the horizontal dimension (left to right), and depth is the vertical dimension (top to bottom). Depth has much more impact on beam strength because strength is proportional to depth squared. A deeper beam is much stronger than a wider beam.
What wood grade should I use?
Standard construction typically uses #2 grade lumber, which has an allowable bending stress of about 900 psi. Higher grades (#1: 1200 psi, Select Structural: 1450 psi) are stronger but cost more. Use higher grades for longer spans or higher loads.
What is the L/360 deflection limit?
L/360 means the beam can deflect no more than the span length divided by 360. For a 12-foot span, maximum deflection is 12×12/360 = 0.4 inches. This prevents excessive bounce or sag in floors. Exceeding this limit can cause discomfort and damage.
Can I use this calculator for critical structures?
This calculator provides simplified engineering estimates for planning and preliminary design. For critical structural applications, load-bearing walls, or commercial buildings, always consult a licensed structural engineer who can perform detailed analysis considering actual wood species, moisture content, loading conditions, and local building codes.
What if my beam shows as inadequate?
If the beam shows as inadequate (safety factor < 100% or deflection exceeds limit), increase beam depth (most effective), use higher wood grade, or reduce span length. Depth has the most impact on beam strength. Always ensure adequate safety margins for structural applications.