Wood Beam Span Calculator
Wood Beam Span Calculator
To use wood bean span calculator, enter your beam dimensions (width and depth in inches). Select wood species, Input expected load type (live load, dead load) and specify beam spacing.
The calculator displays maximum allowable span, wood species, load type, and additional notes.
Floor Joist
- Beam Width: 2 inches
- Beam Height: 10 inches
- Wood Species: Douglas Fir (
E = 1,900,000 psi
)- Load Type: Live Load (40 lbs/ft)
- Spacing: 16 inches
- Result: Maximum Span = 12.5 feet
How to Calculate Wood Beam Span
To determine beam dimensions, begin by measuring the width (b) and height (h) of wood beam. Next, select type of wood you will use and note its modulus of elasticity (E). With these measurements, calculate moment of inertia using the formula I = (b * h^3) / 12.
Then, input uniformly distributed load (w) and spacing between beams. Finally, compute the maximum allowable span using the appropriate span formula.
Deck Beam
- Beam Width: 3 inches
- Beam Height: 12 inches
- Wood Species: Southern Pine (
E = 1,800,000 psi
)- Load Type: Total Load (60 lbs/ft)
- Spacing: 24 inches
- Result: Maximum Span = 10.8 feet
Beam Span Formula
Maximum Span = √((96 × Fb × S) ÷ (w × spacing))
Where:
Fb = Allowable Fiber Stress (psi)
S = Section Modulus (in³)
w = Total Load (psf)
spacing = Beam Spacing (ft)
Section Modulus (S) = (width × depth²) ÷ 6
Deflection = (5 × w × L⁴) ÷ (384 × E × I)
The formula requires:
- Beam Dimensions: Width and depth
- Wood Species: Fiber stress rating
- Load Values: Live and dead loads
- Beam Spacing: Distance between beams
Standard Floor Joist
- Inputs: Beam size = 2×10 (1.5″ × 9.25″), Wood species = Douglas Fir (#2, Fb = 1,500 psi), Live load = 50 psf, Dead load = 15 psf, Spacing = 24 inches
- Calculations: Section Modulus, S = (1.5 × 9.25²) ÷ 6 = 21.4 in³. Maximum Span = √((96 × 1,500 × 21.4) ÷ (65 × 2)) = 14.2 feet
- Result: The maximum allowable span is 14.2 feet
Deck Support Beam
- Inputs: Beam size = 2×8 (1.5″ × 7.25″), Wood species = Southern Pine (#2, Fb = 1,800 psi), Live load = 40 psf, Dead load = 10 psf, Spacing = 16 inches
- Calculations: Section Modulus, S = (1.5 × 7.25²) ÷ 6 = 13.1 in³. Maximum Span = √((96 × 1,800 × 13.1) ÷ (50 × 1.33)) = 12.8 feet
- Result: The maximum allowable span is 12.8 feet
Ceiling Joist
- Inputs: Beam size = 2×6 (1.5″ × 5.5″), Wood species = Hem-Fir (#2, Fb = 1,300 psi), Live load = 20 psf, Dead load = 10 psf, Spacing = 12 inches
- Calculations: Section Modulus, S = (1.5 × 5.5²) ÷ 6 = 7.6 in³. Maximum Span = √((96 × 1,300 × 7.6) ÷ (30 × 1)) = 9.6 feet
- Result: The maximum allowable span is 9.6 feet
Heavy Load Beam
- Inputs: Beam size = 2×12 (1.5″ × 11.25″), Wood species = Southern Pine (#2, Fb = 1,800 psi), Live load = 60 psf, Dead load = 20 psf, Spacing = 16 inches
- Calculations: Section Modulus, S = (1.5 × 11.25²) ÷ 6 = 31.6 in³. Maximum Span = √((96 × 1,800 × 31.6) ÷ (80 × 1.33)) = 15.4 feet
- Result: The maximum allowable span is 15.4 feet
Light Load Joist
- Inputs: Beam size = 2×4 (1.5″ × 3.5″), Wood species = Spruce-Pine-Fir (#2, Fb = 1,100 psi), Live load = 30 psf, Dead load = 10 psf, Spacing = 12 inches
- Calculations: Section Modulus, S = (1.5 × 3.5²) ÷ 6 = 3.1 in³. Maximum Span = √((96 × 1,100 × 3.1) ÷ (40 × 1)) = 6.2 feet
- Result: The maximum allowable span is 6.2 feet
What is Wood Beam Span?
A Wood Beam Span represents the maximum safe distance a wooden beam can extend between support points while maintaining structural integrity. The span capacity depends on the beam size, wood type, and load requirements. The calculation considers both permanent loads (building materials) and temporary loads (people, furniture). Critical factors include the beam’s dimensions, wood species strength, and intended use (floors, roofs, decks).