Square Tube Size Calculation

Square tubes (SHS steel) are a common building material widely used in construction, machinery manufacturing, and other fields. They are typically made by bending cold-rolled and hot-rolled steel sheets. Their hollow structure gives them high strength and compressive strength, while also being lightweight, easy to process, and available in various specifications.

To facilitate engineering design, procurement, and processing, it is crucial to accurately understand the methods for calculating square tube dimensions, weight formulas, cross-sectional area calculations, and standard specifications. This article provides a complete guide to square tube dimension calculation.

Square Tube Sizes Parameters

The basic dimensions of a square tube are typically composed of the following parameters:

1. Outer Side Length (A)

The side length of the square cross-section of the tube, such as 50 in 50×50mm.

2. Wall Thickness (t)

The wall thickness of the tube, such as t = 2.0 mm.

3. Inner Side Length (B)

B = A − 2t

4. Length (L)

Commonly 6 m, but can also be customized upon request.

5. Theoretical Weight

Calculated based on cross-sectional area and density.

Square Tube Size Classification

Square tubes are a common building material, frequently used in frame structures, supporting structures, and interior decoration. Based on size, square tubes can be classified into the following three types:

1. Small-sized square tubes

Width ≤ 20mm, Height ≤ 40mm, Thickness ≤ 2.0mm.

2. Medium-sized square tubes

Width 20mm~200mm, Height 40mm~400mm, Thickness 2.0mm~12.0mm.

3. Large-sized square tubes

Width ≥ 200mm, Height ≥ 400mm, Thickness ≥ 12.0mm.

Formulas for Calculating the Size of Square Tubes

1. Calculating formula of square tube inner side length

The formula for calculating the inner side length B is:

B = A – 2t

Where,

A = Outer side length

t = Wall thickness

Example:

Outer side length 50mm, wall thickness 2mm

B = 50 − 2×2 = 46 mm

2. Square tube length calculating formula

Standard length:

6m (most commonly used)

12m Processing lengths: 3m, 4.5m, 5.8m, 8m, etc.

Actual project length calculation method:

L1 = L2 − L3

Where,

L1 = Effective length

L2 = Total length

L3 = Cutting allowance

The cutting allowance is usually 2–5mm (depending on the saw blade type).

3. Calculating formula of square tube wall thickness

The wall thickness of a square tube refers to its physical thickness, usually expressed in millimeters.

Its calculation method is:

Wall thickness = (Outer diameter - Inner diameter) ÷ 2

Where both the outer and inner diameters are in millimeters.

For example:

A square tube with an outer diameter of 60mm and an inner diameter of 50mm has a wall thickness of 5mm.

4. Calculating formula of square tubes cross-sectional area

The cross-sectional area of a square tube can be calculated using the following formula:

S = A² − (A − 2t)² = (4At − 4t²)

Where,

A = Outer side length

t = Wall thickness

Example:

50×50×2.0 square tube

S = 4×50×2 − 4×2² = 400 − 16 = 384 mm²

5. Square tube perimeter calculating formula

The outer perimeter P of a square tube can be calculated using the following formula:

P = 4A

Where,

A = Outer side length

Example:

A = 100 mm

P = 4×100 = 400 mm

6. Square tube weight calculating formula

The weight of a square tube refers to the weight of each tube, usually expressed in kilograms.

Theoretical Weight Formula:

W=S×L×ρ

Where,

ρ = Density (generally 7.85×10⁻⁶ kg/mm³ for carbon steel)

L = Length (mm)

General Formula (in meters):

W (kg)=0.0157×(A−t)×t×L

(Commonly used industry empirical formula)

Example:

100×100×4.0, length 6m

W=0.0157×(100−4)×4×6=22.64 kg

Standard Sizes of Square Tubes

In addition to the sizes calculated using the above formulas, square tubes also have some common standard sizes.

For example, international standards include 50×25mm, 80×40mm, and 100×50mm, while Chinese standards include 40×30mm, 70×50mm, and 100×80mm.

When selecting square tubes, you can choose the appropriate size according to your actual needs.

How to Choose the Appropriate Square Tube Size?

1. Consider the stress conditions of square tubes

As a structural material, square tubes need to withstand certain loads during use.

Therefore, when selecting the size of square tubes, we need to fully consider their stress conditions, including static loads, dynamic loads, and impact loads.

Generally speaking, larger square tubes with stronger load-bearing capacity are suitable for applications with larger loads, while smaller square tubes are more suitable for light loads or auxiliary support scenarios.

2. Analyze the usage environment and requirements

The usage environment of square tubes is also an important factor to consider when selecting sizes.

For example, square tubes used in humid or corrosive environments should be selected based on materials and sizes with good rust and corrosion resistance.

Furthermore, for applications requiring frequent movement or disassembly, smaller, lighter-weight square tubing may be more suitable due to its portability.

3. Choosing based on cost budget

While meeting usage requirements, we also need to consider the cost budget when selecting square tubing size.

Generally, larger square tubing uses more material, resulting in higher costs.

With a limited budget, we can reduce reliance on larger square tubing by optimizing structural design and selecting high-strength materials, thereby effectively controlling costs.

FAQ

1. How is the wall thickness of the square tubing determined?

The wall thickness is determined by the design load, mechanical requirements, and the usage environment.

Common wall thickness ranges:

Small square tube: 1.0–2.0mm

Medium square tube: 2.0–4.0mm

Large structural square tube: 4.0–12.0mm

2. What are the standard dimensions for square tubes?

Common standards include:

GB/T 6728 (China)

EN 10219 (European standard)

ASTM A500 (American standard)

The three standards differ slightly in their dimensional settings.

3. What are the dimensional differences between SHS steel and RHS steel?

Square tube (SHS steel): A = A (square cross-section)

Rectangular tube (RHS steel): A ≠ B (rectangular cross-section)

Rectangular tubes exhibit more pronounced directional bending resistance.

Square tubes have more uniform overall compressive strength.

Read more: SHS steel meaning