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Beam Deflection Calculator

Calculate maximum deflection for simply supported and cantilever beams under point load.

Select the beam support condition.
Span length in feet.
Total load in pounds.
Section property from beam tables.
Beam Type Simply Supported
Max Deflection 0.0124 in
Deflection (in) 0.0124
L/Δ Ratio L/9666.7
Editorial Standard

GetCalcu Methodology & Editorial Standards

Reviewed: September 2026

American Institute of Steel Construction (AISC) & classical Euler-Bernoulli beam theory deflection formulations.

Reference Sources: GetCalcu Structural Engineering Review Board

Understanding Beam Deflection in Structural Engineering

Beam deflection is the degree to which a beam bends under load. Excessive deflection can damage finishes and affect structural integrity.

The Deflection Formula

Deflection depends on load, span length, material stiffness (E), and cross-section shape (I). The formulas differ for simply supported and cantilever beams.

Allowable Deflection Limits

Building codes typically limit deflection to L/360 for live loads and L/240 for dead loads. For a 10 ft beam, that is about 0.33 inches for live load.

Increasing Stiffness

To reduce deflection, increase the moment of inertia (deeper beam), use a stiffer material (steel vs wood), add supports, or reduce the span.

How to Use the Beam Deflection Calculator

  1. 1
    Select beam type.
  2. 2
    Enter beam length, load, and moment of inertia.
  3. 3
    Review maximum deflection and L/Δ ratio.

Beam Deflection Calculator Formula

δ = (P × L³) / (48 × E × I) [simply] | δ = (P × L³) / (3 × E × I) [cantilever]

Real-World Worked Examples

These scenarios demonstrate how key input parameters alter your calculation outcome.

Wood Beam

Input: Simply supported, 10 ft, 1000 lbs, I = 100 in⁴
Result: δ ≈ 0.0106 in, L/δ ≈ 11320

Steel Cantilever

Input: Cantilever, 8 ft, 500 lbs, I = 200 in⁴
Result: δ ≈ 0.0030 in, L/δ ≈ 31900

Frequently Asked Questions

What is moment of inertia?

Moment of inertia (I) measures a beam resistance to bending. It depends on the cross-section shape. Deeper beams have much higher I than wider beams of the same area.

What is the modulus of elasticity?

E (modulus of elasticity) measures material stiffness. Steel is about 29,000,000 psi. Wood is about 1,500,000–1,800,000 psi depending on grade.

What is L/360?

L/360 is a common deflection limit. It means the maximum deflection should not exceed the span length divided by 360. For a 10 ft span, that is 0.33 inches.

Can I use this for steel beams?

Yes, but ensure you use the correct moment of inertia for the steel section. This calculator uses E = 29,000,000 psi, which is standard for steel.