Technical guide
Square tube weight: formula, examples and table
Freight, quotation and structural checks all start from weight per metre. The formula is simple, but the tolerance is where invoices drift — thin-wall tube can legally weigh 10 % less.
Technical guide
Freight, quotation and structural checks all start from weight per metre. The formula is simple, but the tolerance is where invoices drift — thin-wall tube can legally weigh 10 % less.
For a square hollow section with outside size a (mm) and wall t (mm):
weight (kg/m) = 4 × (a − t) × t × 0.00785For a rectangular section a × b:
weight (kg/m) = 2 × ((a + b) − 2t) × t × 0.007850.00785 is the density of steel in kg/cm³ expressed for millimetre inputs.
200×200×8:
4 × (200 − 8) × 8 × 0.00785 = 48.3 kg/mA 12 m length weighs 579 kg. A 40HQ container of 25 t therefore holds about 43 lengths of this size — which is exactly the kind of number that decides your freight per tonne.
| Size (mm) | Wall (mm) | kg/m | kg per 12 m |
|---|---|---|---|
| 50×50 | 2.0 | 3.01 | 36.1 |
| 50×50 | 3.0 | 4.43 | 53.2 |
| 80×80 | 3.0 | 7.25 | 87.0 |
| 100×100 | 4.0 | 12.1 | 145 |
| 150×150 | 6.0 | 27.1 | 325 |
| 200×200 | 8.0 | 48.3 | 579 |
| 300×300 | 10.0 | 91.1 | 1,093 |
| 400×400 | 12.0 | 146 | 1,755 |
Full matrix: catalogue with all 31 sizes.
The formula gives theoretical weight. Real bundles differ because:
For container loading we quote actual bundle weight from the packing list, not the theoretical figure, so the shipping documents and the invoice agree.
Usually yes when declared as theoretical, but the packing list weight must match the actual bundle weight within the carrier's tolerance.
Wall tolerance. A −10 % wall on 8 mm is 7.2 mm, which cuts roughly 10 % of the weight — legal under GB/T 6728 and EN 10219.
Yes, the packing list with bundle weights and container loading plan is issued before departure.