TECHNICAL 07 · MATERIAL
Tube weight: the formula, the tolerance, and how to check a bill of materials.
Weight per metre is how buyers compare tube prices and how forwarders plan a container. The geometric formula is simple; the difference between calculated and mill-table weight is where purchase orders go wrong.
| Section | Formula (kg/m) | Notes |
|---|---|---|
| Round | 0.02466 × t × (D − t) | D and t in mm; exact for plain round |
| Square | 4 × (a − t) × t × 0.00785 | ignores corner radii, ≈ +2–3 % vs mill table |
| Rectangular | 2 × (a + b − 2t) × t × 0.00785 | same caveat |
| Oval | perimeter (Ramanujan approx) × t × 0.00785 | approximate; oval tables vary by mill |
0.00785 kg/m per mm² of section area, i.e. steel density 7.85 g/cm³.
Worked examples
| Section | Calculation | Result |
|---|---|---|
| Ø60.3 × 2.0 | 0.02466 × 2.0 × 58.3 | 2.87 kg/m |
| Ø48.3 × 2.0 | 0.02466 × 2.0 × 46.3 | 2.28 kg/m |
| 40 × 40 × 2.0 | 4 × 38 × 2 × 0.00785 | 2.39 kg/m (table ≈ 2.31) |
| 30 × 60 × 2.0 oval | approx perimeter 142 mm × 2 × 0.00785 | ≈ 2.23 kg/m |
If a quotation's weight per metre is 10 % above these, ask whether it is a different wall thickness.
Why calculated and mill weights differ
- Corner radii: a square tube's rounded corners remove area, so the geometric formula overestimates.
- Wall tolerance: EN 10219 allows a wall thickness tolerance, so a “2.0 mm” tube may be lighter.
- Zinc: coating adds a few percent to shipping weight, which matters at container limits.
- Oval: the perimeter depends on the actual shape, and mills publish their own tables.
How to use this when buying
Ask for weight per metre per member and compare against the formula. A frame quoted at 6.5 kg/m² where the formulas suggest 4.5 kg/m² is either a heavier design or a padded number — both worth a question.
Weight and the container
Container payload, not volume, usually binds first on steel. A 40HQ carries roughly 26–27 t payload; a frame at 6 kg/m² for 1,000 m² is about 6 t of steel, so the frame fills the container by volume long before it reaches the weight limit. The exception is heavy-wall profiles and fittings, where weight becomes the constraint.
Read next
Pages that answer the question this page raises.
- 10.01Tube weight calculatorCalculate steel tube weight per metre: round, oval, square and rectangular tube, with per-→
- 04.01Round steel tubeRound galvanised steel tube for greenhouses: 1/2″ to 4″ outside diameter, wall 1.0–4.0 mm,→
- 04.02Oval arch tubeOval steel tube for greenhouse arches: 30×60, 30×70, 40×80, 40×90, 50×100 mm, wall 1.5–2.5→
- 08.09Container loadingGreenhouse frame container loading: 20GP and 40HQ internal dimensions, 6 m and 12 m tube, →
NEXT STEP
Turn this into a quoted frame list
If this page answered the technical question, the next step is a number. Send the parameters and we will price the tube, profiles, gutters and fittings as one package.