What is beam deflection?

Deflection is how much a beam bends under load. It's measured at the point of maximum displacement, typically the center for simply supported beams. Excessive deflection causes cracking, bouncy floors, and structural damage.

What is acceptable beam deflection?

Common limits: L/360 for floors with brittle finishes (plaster), L/240 for general floors, L/180 for roofs. For a 4m span, L/360 = 11.1mm maximum deflection.

How do I calculate moment of inertia?

For rectangular beams: I = (b × h³) / 12, where b is width and h is height. Doubling height increases I by 8×. For I-beams and other shapes, use standard tables.

What's the difference between simple and cantilever beams?

Simply supported beams rest on supports at both ends. Cantilever beams are fixed at one end and free at the other. Cantilevers deflect more and have higher stress for the same load and span.

How does beam height affect strength?

Beam strength increases with the square of height (h²) for stress, and deflection decreases with the cube of height (h³). Doubling height makes a beam 4× stronger and 8× stiffer.

What is bending stress?

Bending stress is the internal stress caused by bending moment. Maximum stress occurs at the top and bottom surfaces. Formula: σ = M × c / I, where M is moment, c is distance from neutral axis, I is moment of inertia.

Beam Load Calculator

Our beam load calculator helps engineers, architects, and builders analyze structural beams. Enter beam dimensions, material properties, and loading conditions to calculate deflection, stress, and safety factors. Essential for deck building, floor joists, and structural design.

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calendar_today Updated: April 2025

auto_awesome AI Insights AI

New

Beam Type

Material

Span

Load

kg/m

Width

Height

100mm

200mm

Status

check_circle

Deflection

12.5 mm

L/320

Max Stress

7.5 MPa

Allow: 10 MPa

Safety Factor 1.33

01.01.52.0+

Moment:2.45 kN·m

Inertia:66.7M mm⁴

Input Values

Beam Type

Simply Supported

Cantilever

Material

Wood (Pine/Fir)

Wood (Oak/Hardwood)

Steel

Aluminum

Span Length

Load

kg/m

Beam Width

Beam Height

auto_awesome AI Analysis

Enter your values and calculate to receive AI-powered insights about your results.

straighten Common Floor Loads

Residential 40 PSF

Office 50 PSF

Retail 75 PSF

Storage 125+ PSF

safety_check Safety Factors

🏗️ Steel: 1.5 - 2.0
🪵 Wood: 2.0 - 3.0
🧱 Concrete: 2.0 - 2.5

How to Use This Calculator

Select Beam Type

Choose simply supported or cantilever configuration

Choose Material

Select wood, steel, or aluminum

Enter Dimensions

Input span length and cross-section dimensions

Specify Load

Enter the distributed or point load

Review Results

Check deflection, stress, and safety factor

The Formula

For a simply supported beam with uniform load, deflection depends on load, span length (to the 4th power), and beam stiffness (E×I). Acceptable deflection is typically L/360 for floors or L/240 for roofs.

δ = (5 × w × L⁴) / (384 × E × I)

lightbulb Variables Explained

δ Maximum deflection at center
w Distributed load (N/m or lb/ft)
L Beam span length
E Modulus of elasticity (material stiffness)
I Moment of inertia (beam cross-section)

tips_and_updates Pro Tips

Deflection limit: L/360 for floors with plaster ceiling, L/240 for general floors

Always check both deflection AND stress limits

Wood beams: typical allowable stress is 10-15 MPa for construction lumber

Steel beams: typical yield stress is 250-350 MPa

Cantilever beams deflect more than simply supported beams of same span

Doubling beam height reduces deflection by 8× (height affects I as h³)

Consider dynamic loads (people walking) with impact factor 1.5-2.0

Beam analysis involves calculating deflection (how much it bends) and stress (internal forces). Both must be within acceptable limits for safe design.

For floors, use L/360 deflection limit. Increase beam height for longer spans. Steel beams are stronger but heavier than wood. Consider composite beams for optimal performance.