Square tube is a hollow structural section with four approximately equal outer sides. Compared with round tube, square tube provides four flat surfaces, making it convenient for structural connections, welding, fabrication, and frame construction.
Square tubes are widely used in construction, structural frames, machinery, solar mounting systems, agricultural structures, fencing, equipment frames, and general fabrication.
What Is a Square Tube?
A square tube is a closed hollow section with a square-shaped cross-section.
The main dimensions and specifications include:
- Outside Dimension
- Wall Thickness
- Inside Dimension
- Corner Radius
- Length
- Cross-sectional Area
- Mass per Unit Length
| Parameter | Value |
| Outside Dimension | 100 × 100 mm |
| Wall Thickness | 5 mm |
| Nominal Inside Dimension | 90 × 90 mm |
| Cross Section | Square |
| Length | According to order |
Square Tube vs. Square Pipe
The terms square tube and square pipe are sometimes used interchangeably in commercial markets, but they can have different meanings in engineering applications.
The term pipe is more commonly associated with fluid transportation, pressure systems, and piping standards.
The term tube is more frequently used for structural, mechanical, and fabrication applications. Tubes are generally specified by their outside dimensions and wall thickness.
In practical applications, square tubes are frequently used in structural and mechanical manufacturing; however, when purchasing them, the focus is not on the distinction between “pipe” and “tube,” but rather on product standards and technical specifications.
Square Tube Sizes and Dimensions
Square Tube Sizes Charts
The following table provides representative dimensions and unit masses for smaller square hollow sections based on data listed in EN 10219-2.
| Outside Dimension | Wall Thickness | Approx. Mass |
| 20 × 20 mm | 2.0 mm | 1.05 kg/m |
| 25 × 25 mm | 2.0 mm | 1.36 kg/m |
| 25 × 25 mm | 2.5 mm | 1.64 kg/m |
| 25 × 25 mm | 3.0 mm | 1.89 kg/m |
| 30 × 30 mm | 2.0 mm | 1.68 kg/m |
| 30 × 30 mm | 2.5 mm | 2.03 kg/m |
| 30 × 30 mm | 3.0 mm | 2.36 kg/m |
| 40 × 40 mm | 2.0 mm | 2.31 kg/m |
| 40 × 40 mm | 2.5 mm | 2.82 kg/m |
| 40 × 40 mm | 3.0 mm | 3.30 kg/m |
| 40 × 40 mm | 4.0 mm | 4.20 kg/m |
| 50 × 50 mm | 2.0 mm | 2.93 kg/m |
| 50 × 50 mm | 2.5 mm | 3.60 kg/m |
| 50 × 50 mm | 3.0 mm | 4.25 kg/m |
| 50 × 50 mm | 4.0 mm | 5.45 kg/m |
| 50 × 50 mm | 5.0 mm | 6.56 kg/m |
| 60 × 60 mm | 2.0 mm | 3.56 kg/m |
| 60 × 60 mm | 2.5 mm | 4.39 kg/m |
Square tubes of the same dimensions can be paired with different wall thicknesses; for example, a 50 × 50 mm square tube may be available with a wall thickness of 2.0, 2.5, 3.0, 4.0, or 5.0 mm.
Square Tube Wall Thickness
Wall thickness is a critical parameter for square tubes; increasing it results in higher sectional stiffness and a larger section modulus, while also improving resistance to local buckling.
The following example uses a 50 × 50 mm square tube with different nominal wall thicknesses.
| Wall Thickness | Cross-Sectional Area | Approx. Mass | Moment of Inertia, I | Section Modulus, Z | Radius of Gyration |
| 2.0 mm | 384 mm² | 3.01 kg/m | 147,712 mm⁴ | 5,908 mm³ | 19.61 mm |
| 2.5 mm | 475 mm² | 3.73 kg/m | 179,115 mm⁴ | 7,165 mm³ | 19.42 mm |
| 3.0 mm | 564 mm² | 4.43 kg/m | 208,492 mm⁴ | 8,340 mm³ | 19.23 mm |
| 4.0 mm | 736 mm² | 5.78 kg/m | 261,525 mm⁴ | 10,461 mm³ | 18.85 mm |
| 5.0 mm | 900 mm² | 7.07 kg/m | 307,500 mm⁴ | 12,300 mm³ | 18.48 mm |
1.The section properties below are theoretical geometric values calculated from the nominal dimensions, using a sharp-corner approximation. Actual manufactured values may differ because real square tubes have corner radii and dimensional tolerances.
2.The mass values in this table are theoretical values calculated using a steel density of approximately 7,850 kg/m³.
As can be seen from the table above:
Cross-sectional area increases from 384 to 900 mm², an increase of approximately 134%.
Moment of inertia increases from 147,712 to 307,500 mm⁴, an increase of approximately 108%.
Section modulus increases from 5,908 to 12,300 mm³, an increase of approximately 108%.
Theoretical mass increases from approximately 3.01 to 7.07 kg/m, an increase of approximately 135%.
To learn more about the materials and properties of square tubes, please visit our “Square Tube Specifications | Size and Materials | Solar Frame” page. You can contact us directly via email to purchase square tubes.
