Mechanical Engineering Calculator

Cantilever Beam Calculator

Calculate reactions, shear force, bending moment, deflection and bending stress for a cantilever beam with a point load at the free end.

Beam Configuration

Cantilever beam with point load at the free end — fixed at left, free at right

P = 5000 NDeflected shapeL = 2000 mmFixedFree

Input Parameters

Enter values using the SI-derived N-mm unit system.

N

Concentrated load applied at the free end.

mm

Length from fixed support to free end.

MPa

Young's modulus of the beam material.

mm⁴

Area moment of inertia about the bending axis.

mm

Optional – required only for bending stress.

mm

User-defined maximum allowable deflection.

MPa

User-defined maximum allowable bending stress.

Engineering Tip

Cantilevers develop significantly higher moments and deflections than simply supported beams of the same span. Always verify both the fixed-end moment capacity and the free-end deflection.

Maximum Deflection (Free End)

44.444mm

Deflection / Span = 1 / 45

Reaction

5,000.0 N

Max Shear

5,000.0 N

Max Moment

10,000,000 N·mm

Max Stress

333.333 MPa

FAIL — Deflection exceeds the allowable limit

Calculated deflection is 44.444 mm vs limit of 25 mm.

FAIL — Stress exceeds the allowable limit

Calculated stress is 333.333 MPa vs limit of 250 MPa.

Governing Formulas

R = P
Vmax = P
Mmax = P L
δmax = P L³ / (3 E I)
σmax = M c / I

Calculation Assumptions

  • Cantilever (fixed-free) beam
  • Point load at free end only
  • Linear elastic material
  • Small deflection theory
  • Constant cross-section
  • Negligible self-weight (or included in P)

Engineering Code

Reuse the complete analysis in your own engineering workflow.

Python
def cantilever_beam(P, L, E, I, c=None):
    """
    Complete analysis of a cantilever beam
    with a point load at the free end.

    P: Load (N)
    L: Beam length (mm)
    E: Elastic modulus (MPa)
    I: Area moment of inertia (mm⁴)
    c: Distance to extreme fiber (mm) – optional

    Returns dict with reaction, shear, moment, deflection, stress
    """

    if P <= 0 or L <= 0 or E <= 0 or I <= 0:
        raise ValueError("P, L, E, I must be greater than zero.")

    reaction = P
    shear = P
    moment = P * L
    deflection = (P * L**3) / (3 * E * I)
    stress = (moment * c) / I if c and c > 0 else None

    return {
        "reaction_N": reaction,
        "shear_N": shear,
        "moment_Nmm": moment,
        "deflection_mm": deflection,
        "stress_MPa": stress
    }


# Example
P = 5000
L = 2000
E = 200000
I = 1500000
c = 50

results = cantilever_beam(P, L, E, I, c)
for k, v in results.items():
    print(f"{k}: {v}")
MATLAB
function results = cantilever_beam(P, L, E, I, c)
    % Complete analysis of a cantilever beam
    % with a point load at the free end.
    %
    % P = Load (N)
    % L = Beam length (mm)
    % E = Elastic modulus (MPa)
    % I = Area moment of inertia (mm^4)
    % c = Distance to extreme fiber (mm) – optional

    if P <= 0 || L <= 0 || E <= 0 || I <= 0
        error('P, L, E, I must be greater than zero.');
    end

    results.reaction = P;
    results.shear = P;
    results.moment = P * L;
    results.deflection = (P * L^3) / (3 * E * I);
    if nargin >= 5 && c > 0
        results.stress = (results.moment * c) / I;
    else
        results.stress = NaN;
    end
end

% Example
P = 5000;
L = 2000;
E = 200000;
I = 1500000;
c = 50;

r = cantilever_beam(P, L, E, I, c);
disp(r);
Excel Formulas
Reaction: =P
Shear: =P
Moment: =P*L
Deflection: =(P*L^3)/(3*E*I)
Stress: =(M*c)/I

Example Calculation

Cantilever beam with P = 5,000 N at the free end, L = 2,000 mm, E = 200,000 MPa, I = 1,500,000 mm⁴, c = 50 mm:

R = 5,000 N
Vmax = 5,000 N
Mmax = 10,000,000 N·mm
δmax = 22.222 mm
σmax = 333.333 MPa

Technical Explanation: Cantilever Beam Analysis

A cantilever beam is fixed at one end and free at the other. The fixed end provides both a vertical reaction force and a restraining moment, making the beam statically determinate under transverse loading.

When a concentrated point load acts at the free end, the shear force is constant along the entire length, while the bending moment increases linearly from zero at the free end to its maximum value at the fixed support. The maximum deflection and slope also occur at the free end.

How to Use This Calculator

  1. Point Load (P): Enter the concentrated load applied at the free end in Newtons (N).
  2. Beam Length (L): Enter the length from the fixed support to the free end in millimeters (mm).
  3. Elastic Modulus (E): Material stiffness in MPa (e.g. 200,000 for structural steel).
  4. Moment of Inertia (I): Area moment of inertia in mm⁴.
  5. Distance to Extreme Fiber (c) – Optional: Required only if you want bending stress (mm).

Key Formulas Used

  • Vertical reaction: R = P
  • Maximum shear force: Vmax = P
  • Maximum bending moment: Mmax = P L (at fixed end)
  • Maximum deflection: δmax = P L³ / (3 E I) (at free end)
  • Maximum bending stress: σmax = M c / I

Cantilever vs Simply Supported

For the same load and length, a cantilever develops four times the maximum moment and sixteen times the maximum deflection of a simply supported beam with a central point load. This is why cantilevers are generally limited to shorter spans or lighter loads.

Real-World Engineering Cases

Balcony and Canopy Failures

Several residential balcony collapses have been traced to underestimation of the fixed-end moment and inadequate reinforcement or connection detailing at the wall or beam support. The high moment concentration at the root was not properly designed for.

Engineering Lesson

The fixed end of a cantilever is a critical section. Both the moment capacity and the connection (or embedment) must be verified with appropriate safety factors and construction quality control.

Overhanging Sign and Billboard Structures

Large cantilevered advertising structures have failed under wind load when the design used only static gravity loads. The combination of self-weight moment and wind-induced moment at the fixed base exceeded capacity.

Engineering Lesson

Cantilevers are sensitive to both gravity and lateral loads. Always include environmental loads (wind, snow, ice) and dynamic effects when analysing outdoor cantilever structures.

Frequently Asked Questions

What does this calculator compute?

It computes the fixed-end reaction, maximum shear force, maximum bending moment, maximum deflection and (optionally) maximum bending stress for a cantilever beam with a point load at the free end.

What are the governing formulas?

R = P, V_max = P, M_max = PL, δ_max = PL³/(3EI), σ_max = Mc/I.

Where do the maximum values occur?

Maximum shear and moment occur at the fixed end. Maximum deflection and slope occur at the free end.

What units should I use?

N for load, mm for length and c, MPa for elastic modulus, mm⁴ for moment of inertia. Results are given in N, N·mm, mm and MPa.

Can I use this for uniform distributed load?

No. This calculator is limited to a single concentrated load at the free end. For uniform load the formulas change (M_max = wL²/2, δ_max = wL⁴/8EI).

Engineering calculations provided by this tool are for educational and preliminary design purposes. Always verify calculations, loading conditions, material properties, applicable standards, safety factors, and design requirements before using results in a final engineering design.