Square & Rectangular Tube Weight Formula (Metric & Imperial)

Calculating the theoretical weight of a tube is essential for material estimation, shipping costs, and structural design. This guide provides the exact calculation formulas for Square Tubes (SHS), Rectangular Tubes (RHS), and Round Pipes (CHS) in both metric (kg/m) and imperial (lbs/ft) units.

Note: The weight calculated using the formulas below is the theoretical weight. Actual product weight may vary by approximately ±3.5% due to manufacturing tolerances (such as wall thickness variations and corner radii).

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1. Square Tube Formula (SHS)

Metric Formula (kg/m)

For carbon steel square tubes, the most widely used formula in international engineering is:

Weight (kg/m) = [4 × (Side A – Wall Thickness) × Wall Thickness × 0.00785]

● Side A: Outer side length (mm)
● Wall Thickness: (mm)
● 0.00785: Density of carbon steel (g/mm³)

Example Calculation:
For a 100 × 100 × 5 mm square tube:

Weight = [4 × (100 - 5) × 5 × 0.00785] = 14.92 kg/m

(If you need the weight for a 6-meter bar: 14.92 kg/m × 6m = 89.52 kg)

Imperial Formula (lbs/ft)

For the North American market (ASTM A500), the formula using inches is:

Weight (lbs/ft) = [4 × (Side A – Wall Thickness) × Wall Thickness × 0.284]

● Side A: Outer side length (inches)
● Wall Thickness: (inches)
● 0.284: Density of steel (lbs/in³)

Example Calculation:
For a 4" × 4" × 0.250" square tube:
Weight = [4 × (4 - 0.250) × 0.250 × 0.284] = 1.065 lbs/ft

2. Rectangular Tube Formula (RHS)

For rectangular hollow sections, the formula adjusts to account for the two different side lengths (Height and Width):

● Metric Formula (kg/m): 

Weight = [2 × (Height + Width – 2 × Wall Thickness) × Wall Thickness × 0.00785]

● Imperial Formula (lbs/ft): 

Weight = [2 × (Height + Width – 2 × Wall Thickness) × Wall Thickness × 0.284]

(Note: Actual product weight may vary by ±3.5% due to manufacturing tolerances.)

Example:
For a 100 × 50 × 4 mm rectangular tube:
Weight = [2 × (100 + 50 – 8) × 4 × 0.00785] = 8.91 kg/m

3. Round Pipe Formula (CHS)

For clients also dealing with circular hollow sections, the theoretical weight of a round steel pipe is calculated as:

Metric Formula (kg/m):
Weight (kg/m) = (Outer Diameter – Wall Thickness) × Wall Thickness × 0.02466

(Note: Outer Diameter and Wall Thickness must be in mm).

4. Unit Conversion: kg/m to lb/ft

Weight charts published in Asia and Europe typically use kilograms per meter (kg/m), while many North American HSS specifications use pounds per foot (lb/ft). To convert between the two units:

lb/ft = kg/m × 0.67197

Example: A tube weighing 10.80 kg/m is approximately 7.26 lb/ft.

When comparing supplier quotations or international project specifications, always confirm whether the published weight is expressed in kg/m or lb/ft to avoid calculation errors.

5. Quick Reference: Common Sizes & Weights

(If you don't want to calculate manually, here are the weights for the most common sizes)

Square Tube (SHS) Common Weights

Rectangular Tube (RHS) Common Weights

(👉 For a complete list of metric and imperial dimensions, please view our [Square Tube Sizes Chart].)

6. Theoretical Weight vs. Actual Weight

The weights shown in this guide are theoretical values calculated using the standard carbon steel density of 7.85 g/cm³.

In actual production, the measured weight of a tube may vary slightly due to:

● Wall thickness tolerances (usually ±10%)
● Corner radius geometry
● Manufacturing process variations
● Length measurement tolerances

For most structural steel tubes, the difference between theoretical and actual weight is typically within ±3.5% to ±5%. When purchasing steel tubes by tonnage, the actual shipping weight (weighed at the port) should always take precedence over theoretical calculations.

Related Resources

● What is Carbon Steel Square Tube? - Sizes, Grades & Processes
● Square Tube vs. Rectangular Tube Load-bearing Capacity
● Square Tube Sizes & Dimensions Chart (SHS)
● Rectangular Tube Sizes & Dimensions Chart (RHS)

● Square Tube Strength Calculation Formula and Use

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