Short Answer
A 100x100 square pipe with 4 mm wall thickness weighs about 12.06 kg per metre in carbon steel. The weight changes directly with wall thickness: a 3 mm wall gives about 9.09 kg per metre, and a 6 mm wall gives about 17.74 kg per metre. To get an exact value, apply the cross-section formula below using the specified wall thickness and the material density.
Weight Calculation Formula
The weight of a square hollow section is the volume of steel in the wall multiplied by the density of steel. For a square pipe with side length S and wall thickness t, the theoretical weight per metre is calculated as follows:
W = (S squared minus (S minus 2t) squared) multiplied by 7850 / 1000000, in kg per metre, where S and t are in millimetres and 7850 is the density of carbon steel in kg per cubic metre.
For a 100x100 section this becomes: W = (10000 minus (100 minus 2t) squared) multiplied by 0.00785 kg per metre. The term (100 minus 2t) squared is the inside square area, and subtracting it from the outside square area leaves the cross-sectional area of the wall.
Worked Example for 100x100x4
Take a 100x100 square pipe with 4 mm wall. The outside area is 100 by 100, or 10000 square millimetres. The inside square is 92 by 92, or 8464 square millimetres. The wall area is 10000 minus 8464, or 1536 square millimetres. Multiplying by 0.00785 kg per square millimetre per metre gives 12.06 kg per metre. A 6 metre length of this section weighs about 72.3 kg.
Reference Weight Table for 100x100 Square Pipe
| Wall Thickness mm | Theoretical Weight kg/m | Weight per 6 m kg |
|---|---|---|
| 2 | 6.15 | 36.9 |
| 3 | 9.09 | 54.5 |
| 4 | 12.06 | 72.3 |
| 5 | 14.91 | 89.5 |
| 6 | 17.74 | 106.4 |
| 8 | 23.29 | 139.7 |
| 10 | 28.67 | 172.0 |
The table is calculated for carbon steel at 7850 kg per cubic metre. Stainless steel sections weigh about 1 percent more per unit volume, and aluminium sections about one third of the carbon steel weight for the same dimensions.
Standards for Square Hollow Sections
Square pipe and tube are produced to different standards depending on the market and application. ASTM A500 covers cold-formed welded and seamless carbon steel structural tubing in North America, with grades A, B, C and D. EN 10219 covers cold-formed welded structural hollow sections in Europe, with grades such as S235, S275 and S355. GB/T 6728 covers cold-formed welded hollow sections in China, with grades Q235 and Q345. The theoretical weight in the table is the basis for mill pricing and logistics in most markets, and the actual weight tolerance is normally plus or minus 6 percent on a single section.
Why Weight Matters in Practice
Weight determines the freight cost, the lifting capacity needed on site, and the load on the supporting structure. Structural engineers check the self-weight of square pipe members before calculating live loads, and buyers use theoretical weight to confirm the number of pieces that fit in a container. For a 20-foot container, a practical load of around 21 tonnes limits the quantity of 100x100x4 sections to roughly 290 pieces of 6 metres each.
Common Mistakes in Weight Estimation
Using the outside area instead of the wall cross-section.
Ignoring the corner radii, which reduce actual weight slightly below the sharp-corner calculation.
Mixing millimetres and metres in the formula.
Forgetting that galvanized or coated sections add a small extra weight for the coating.
FAQ
Q: How much does 100x100x4 square pipe weigh per metre?
About 12.06 kg per metre in carbon steel. A 6 metre length weighs roughly 72.3 kg.
Q: Does the weight of square pipe depend on the length?
Weight is proportional to length. The per-metre value is fixed for a given wall thickness, and the total weight is the per-metre value multiplied by the length.
Q: What is the formula for square pipe weight?
W = (S squared minus (S minus 2t) squared) multiplied by density, where S is the side length, t is the wall thickness and density is 7850 kg per cubic metre for carbon steel. The result is the weight per unit length in the same unit system.
Q: How much heavier is a stainless steel 100x100 square tube?
Stainless steel density is about 7930 kg per cubic metre, roughly 1 percent higher than carbon steel, so the weight increases by about 1 percent for identical dimensions.
Q: Which standard covers 100x100 square pipe?
The applicable standard depends on the market. ASTM A500 is common in North America, EN 10219 in Europe and GB/T 6728 in China. Confirm the grade and standard when ordering.
Q: Why does the actual delivered weight differ from the table?
Mill tolerances on wall thickness and section size cause small variations. Delivery weight is normally settled on the theoretical weight or the weighed quantity, as agreed in the purchase contract.
