🏗️ Beam Load Calculator
Calculate bending moment, shear force, and deflection for simply supported beams.
Max Bending Moment
How to Use This Calculator
Enter the beam span in feet and the uniform load in pounds per linear foot. Choose your beam size from the dropdown or enter custom dimensions. Select the lumber species and grade. The calculator returns the maximum bending moment, shear force at the supports, and midspan deflection, then checks it against the L/360 floor and L/240 roof deflection limits.
Enter the beam span: the clear distance between the two supports in feet. For a beam resting on posts 14 feet apart, enter 14.
Enter the uniform load in pounds per linear foot. For a deck beam supporting 10-foot-long joists with a 40 psf deck load: 40 × (10 ÷ 2) = 200 lbs per linear foot of beam.
Choose a beam section. Start with a double 2x10 or double 2x12 and see if it passes. If the deflection check fails, step up to a triple or LVL section.
Check both deflection results. The L/360 limit is required for floors. If the beam fails L/360, you need a larger section or shorter span.
Simply Supported Beam Formulas
E is the modulus of elasticity of the lumber in psi. Douglas Fir-Larch No. 2 has an E of 1,600,000 psi. I is the moment of inertia of the beam cross-section. A deeper beam greatly increases stiffness since depth is cubed in the formula. Doubling beam depth reduces deflection by a factor of 8.
Example Projects
Tips for Your Project
This calculator is an estimation tool for planning and education. For any structural application in a permitted project, a licensed structural engineer must review the design. Building departments require engineered drawings for all load-bearing beams in new construction and major renovations. The cost of an engineering review is a small fraction of the overall project cost and protects you from serious structural problems.
When selecting beam lumber, species and grade matter. Douglas Fir-Larch No. 1 has a higher E value than No. 2, which reduces deflection. LVL (laminated veneer lumber) is the most consistent option and is rated by the manufacturer with guaranteed E values. For long spans over 16 feet or heavy loads over 400 lbs per linear foot, LVL or glulam is typically the right choice over sawn lumber.
Frequently Asked Questions
How do I calculate beam load?
For a simply supported beam with uniform load: Max moment M = wL²/8, Max shear V = wL/2, Max deflection δ = 5wL⁴/(384EI). Where w=load/ft, L=span, E=modulus of elasticity, I=moment of inertia.
What is a safe span for a 2×10 beam?
A triple 2×10 (built-up) beam can typically span 10–14 feet for a 10 ft tributary width under typical residential loads. Always consult IRC span tables and local building codes.
What is the modulus of elasticity for wood?
Douglas Fir-Larch #2: E ≈ 1,600,000 psi. Southern Yellow Pine #2: E ≈ 1,600,000 psi. Hem-Fir: E ≈ 1,300,000 psi. This calculator uses standard residential framing lumber values.
How much deflection is allowed?
The standard limit is L/360 for floors (under live load) and L/240 for roofs. For a 12-foot span, max deflection = 12×12/360 = 0.4 inches for floors.
Is this calculator suitable for structural engineering?
This tool is for estimation and educational purposes only. For any structural application, consult a licensed structural engineer. Building codes require engineered designs for load-bearing members.