Enter Square Tube Details
Example Data Table
| Outer Size | Wall | Span | Support | Load Type | Yield Strength | Safety Factor |
|---|---|---|---|---|---|---|
| 2 in | 0.125 in | 6 ft | Simply supported | Point load | 36,000 psi | 2.0 |
| 3 in | 0.1875 in | 8 ft | Simply supported | Uniform total load | 46,000 psi | 2.5 |
| 4 in | 0.25 in | 10 ft | Fixed fixed | Uniform total load | 50,000 psi | 3.0 |
Formula Used
The calculator uses hollow square tube section properties and common beam equations.
Inside side: bᵢ = b - 2t
Area: A = b² - bᵢ²
Moment of inertia: I = (b⁴ - bᵢ⁴) / 12
Section modulus: S = I / (b / 2)
Allowable bending moment: M = Fy × S / safety factor
Approximate allowable shear: V = 0.40 × Fy × A / safety factor
Load capacity is checked by bending, shear, and deflection. The smallest value becomes the estimated safe load.
How To Use This Calculator
- Enter the outside square tube size.
- Enter the wall thickness.
- Select the matching unit for tube dimensions.
- Enter the clear span between supports.
- Select the support condition and load pattern.
- Enter yield strength, elastic modulus, and safety factor.
- Set the deflection limit, such as L/360.
- Press the calculate button.
- Download the result as a CSV or PDF file.
Square Tube Load Capacity Guide
Square Tube Load Capacity Guide
Square tube is popular because it is easy to cut, weld, drill, and align. It resists bending in both main directions. That makes it useful for frames, posts, rails, racks, gates, platforms, and light structural supports. A load calculator gives a fast estimate before a design review.
What The Calculator Checks
This tool estimates capacity from tube size, wall thickness, span, steel strength, support condition, and load pattern. It calculates inside width, metal area, moment of inertia, section modulus, bending capacity, shear capacity, and deflection. The smallest safe load is shown as the governing result. That helps you see whether bending stress, web shear, or movement controls the member.
Why Span And Support Matter
Span has a large effect on capacity. A longer span increases bending moment and deflection quickly. A short tube can carry much more load than the same tube over a long opening. Support condition also matters. A fixed end can reduce bending compared with a simple pin support. A cantilever usually carries far less load because the highest moment occurs at the fixed end.
Material And Safety Factor
Yield strength defines when the steel begins to deform permanently. Common mild steel is often entered near 36,000 psi. Stronger tube may use 46,000 psi or 50,000 psi, when verified by supplier data. The safety factor divides the theoretical strength. A higher factor is useful when loads are uncertain, welds are complex, impacts may occur, or people will stand under the member.
Use The Result Carefully
The output is an engineering estimate, not a stamped design. Real projects may need checks for weld strength, bolt holes, local buckling, torsion, corrosion, vibration, concentrated bearing, lateral bracing, fatigue, and code rules. Use actual dimensions and certified material values whenever possible. For occupied structures, lifting devices, public work, or critical supports, ask a qualified engineer to review the design before construction.
Practical Tips
Keep loads centered when possible. Add bracing to reduce unrestrained length. Avoid cutting large holes near moment areas. Use thicker walls when dents or attachments are expected. Compare several tube sizes before buying material. A larger section can improve stiffness and may cost less than repairing a weak frame later.
FAQs
What does square tube load capacity mean?
It is the estimated load a square hollow tube can carry before bending, shear, or deflection reaches the selected limit.
Does wall thickness affect load capacity?
Yes. A thicker wall increases area, inertia, section modulus, and shear resistance. It usually improves both strength and stiffness.
Why does span reduce capacity?
A longer span creates higher bending moment and greater deflection. Capacity can drop quickly as span increases.
Which support type is strongest?
Fixed fixed support often gives higher bending capacity than simple support. A cantilever is usually the weakest case.
What yield strength should I enter?
Use the certified value from the tube supplier. Common mild steel is often estimated near 36,000 psi.
What is a good safety factor?
Many rough checks use 2 or higher. Critical, public, overhead, or uncertain loading may need a larger factor.
Does this replace an engineer?
No. It is an estimating tool. Important structures should be checked by a qualified engineer before construction.
Can I use millimeter dimensions?
Yes. Select millimeters for tube dimensions. The calculator converts them internally for section and beam calculations.