Square Tubing Load Capacity Calculator

Calculator Inputs

Example Data Table

These sample values are illustrative. They assume Fy = 250 MPa, E = 200000 MPa, safety factor = 1.67, and deflection limit = L/360.

Formula Used

This calculator uses standard hollow square beam equations. All dimensions are in millimeters. Stress uses MPa. Loads are returned in newtons and kilonewtons.

1) Inner side of tube
Inner side = Outer side − 2 × Wall thickness

2) Cross-sectional area
A = B² − b²

3) Second moment of area
I = (B⁴ − b⁴) / 12

4) Section modulus
Z = I / (B / 2)

5) Allowable bending moment
M_allow = Fy × Z / Safety Factor

6) Deflection limit
Allowable deflection = L / Deflection Ratio

7) Beam load formulas
Simply supported point load: M = P × L / 4
Simply supported total distributed load: M = W × L / 8
Cantilever end point load: M = P × L
Cantilever total distributed load: M = W × L / 2

8) Deflection formulas
Simply supported point load: δ = P × L³ / (48 × E × I)
Simply supported total distributed load: δ = 5 × W × L³ / (384 × E × I)
Cantilever end point load: δ = P × L³ / (3 × E × I)
Cantilever total distributed load: δ = W × L³ / (8 × E × I)

The calculator compares the stress-limited load and the deflection-limited load. It reports the smaller value as the allowable load.

How to Use This Calculator

Enter the outer side dimension of the square tube. Then enter the wall thickness. Use the clear unsupported span for a simply supported beam. Use the full fixed length for a cantilever.

Next, enter the material yield strength and elastic modulus. For common structural steel, Fy may be near 250 MPa and E is often about 200000 MPa. Then choose a safety factor and a deflection ratio such as L/360.

Select the support type. Then select the load case. A point load means a center load for a simply supported beam or an end load for a cantilever. A distributed load means the total load spread across the full length.

Press the calculate button. The tool will show section properties, allowable moment, load from bending stress, load from deflection, and the controlling allowable load. Export the result with the CSV or PDF buttons when needed.

Square Tubing Load Capacity Guide

Understand the beam estimate

Square tubing is common in frames, supports, work tables, racks, and light structures. Load capacity depends on more than the outside size. Wall thickness matters. Span matters too. Material strength changes the bending limit. Stiffness changes deflection. This calculator combines those inputs into one clear estimate. It uses standard beam math. It finds the section properties of a hollow square tube. Then it checks stress and deflection. The smaller safe load becomes the governing result. That makes the output practical for quick planning and comparison.

Why section properties are important

The second moment of area tells you how strongly the tube resists bending. A deeper or thicker tube usually raises that value fast. Section modulus converts bending moment into stress. Higher section modulus usually means lower bending stress at the same load. Area is also shown for reference. It helps describe the amount of material in the tube. Small changes in wall thickness can create useful gains in stiffness and strength. Long spans do the opposite. They reduce allowable load quickly because bending moment and deflection both rise as length increases.

Read the result correctly

The result section shows two different load limits. The first comes from bending stress. The second comes from deflection. If stress controls, the tube reaches the allowable bending stress before the movement limit. If deflection controls, the tube bends too much first. This distinction matters in practical design. Shelves, rails, and machine supports often feel weak long before the steel yields. That is why serviceability checks are useful. The calculator also shows the approximate mass equivalent under gravity. That helps users compare loads with objects, equipment, or stored items.

Use engineering judgment

This calculator is useful for educational work, early sizing, and fast checks. It is not a replacement for a stamped structural design. Real projects may need checks for local wall buckling, concentrated bearing, weld strength, connection eccentricity, vibration, fatigue, corrosion, and building code rules. Dynamic loads can reduce safe capacity. Poor support conditions can also change results. Always confirm dimensions and units before using the output. For critical work, ask a qualified engineer to review the tube, supports, base material, and full loading pattern.

FAQs