Tube and hollow section weight calculator
Enter the dimensions and the wall thickness — the calculator gives the mass of one piece, of the whole batch and of a running metre. Below are mass tables for the usual commercial sizes, worked out with the corner radii taken into account.
Short answer
Mass per metre of a hollow section is F · ρ / 1000, where
F is the cross-sectional area in mm² and
ρ = 7.85 g/cm³ for steel. For a round tube the
formula shortens to m = π · t · (D − t) · 0.00785 kilograms per
metre. Most asked for: 40×40×3 — 3.30 kg/m, 50×50×3 — 4.25 kg/m,
60×40×3 — 4.25 kg/m, 80×40×4 — 6.71 kg/m; tube 33.7×3.2 —
2.41 kg/m, 42.4×3.2 — 3.09 kg/m, 60.3×3.6 — 5.03 kg/m.
Square and rectangular sections
| Section, mm | A, mm² | Mass, kg/m | 6 m length, kg |
|---|---|---|---|
| 20×20×2 | 134 | 1.05 | 6.3 |
| 25×25×2 | 174 | 1.36 | 8.2 |
| 30×30×2 | 214 | 1.68 | 10.1 |
| 30×30×3 | 301 | 2.36 | 14.2 |
| 40×20×2 | 214 | 1.68 | 10.1 |
| 40×40×2 | 294 | 2.31 | 13.9 |
| 40×40×3 | 421 | 3.30 | 19.8 |
| 40×40×4 | 535 | 4.20 | 25.2 |
| 50×30×3 | 421 | 3.30 | 19.8 |
| 50×50×3 | 541 | 4.25 | 25.5 |
| 50×50×4 | 695 | 5.45 | 32.7 |
| 60×40×3 | 541 | 4.25 | 25.5 |
| 60×40×4 | 695 | 5.45 | 32.7 |
| 60×60×3 | 661 | 5.19 | 31.1 |
| 60×60×4 | 855 | 6.71 | 40.3 |
| 80×40×3 | 661 | 5.19 | 31.1 |
| 80×40×4 | 855 | 6.71 | 40.3 |
| 80×80×4 | 1175 | 9.22 | 55.3 |
| 80×80×5 | 1436 | 11.3 | 67.6 |
| 100×50×4 | 1095 | 8.59 | 51.6 |
| 100×100×4 | 1495 | 11.7 | 70.4 |
| 100×100×5 | 1836 | 14.4 | 86.5 |
| 100×100×6 | 2163 | 17.0 | 101.9 |
| 120×60×4 | 1335 | 10.5 | 62.9 |
| 120×80×5 | 1836 | 14.4 | 86.5 |
| 120×120×5 | 2236 | 17.6 | 105.3 |
| 150×100×5 | 2336 | 18.3 | 110.0 |
| 150×150×6 | 3363 | 26.4 | 158.4 |
Round tubes
| Tube D×t, mm | A, mm² | Mass, kg/m | 6 m length, kg |
|---|---|---|---|
| 21.3×2.6 | 153 | 1.20 | 7.2 |
| 26.9×2.6 | 199 | 1.56 | 9.4 |
| 33.7×3.2 | 307 | 2.41 | 14.5 |
| 42.4×3.2 | 394 | 3.09 | 18.6 |
| 48.3×3.2 | 453 | 3.56 | 21.4 |
| 60.3×3.6 | 641 | 5.03 | 30.2 |
| 76.1×3.6 | 820 | 6.44 | 38.6 |
| 88.9×4.0 | 1067 | 8.38 | 50.3 |
| 114.3×4.5 | 1552 | 12.2 | 73.1 |
| 139.7×5.0 | 2116 | 16.6 | 99.7 |
| 168.3×5.6 | 2862 | 22.5 | 134.8 |
| 219.1×6.3 | 4212 | 33.1 | 198.4 |
The tables are worked out for a density of 7.85 g/cm³. For hollow
sections the EN 10219 formula was used with an outer corner radius of
2t for walls up to 6 mm — which is why they come out
3–7 % below the plain subtraction of rectangles that the calculator above
performs. The product also carries a wall thickness tolerance, so settlement
goes by the certificate.
Cross-section formulas
| Shape | Cross-sectional area |
|---|---|
| Round tube | F = π · t · (D − t) |
| Hollow section, simplified | F = a·b − (a − 2t)·(b − 2t) |
| Hollow section to EN 10219 | F = 2t·(a + b − 2t) − (4 − π)·(r₀² − r₁²) |
In the last formula r₀ is the outer corner radius (taken as
2t for walls up to 6 mm) and r₁ =
r₀ − t. Mass per metre is always F · ρ / 1000
kilograms with F in mm².
Welding hollow sections
The thin wall is the main problem: at 2 mm a burn-through is a matter of a second, and on a corner half a second, because the heat has nowhere to go. Current follows the thinnest part, not the overall size of the section: 40×40×2 is 60–80 A work with a 2.0 mm electrode, or short-arc MAG at 90–110 A with 0.8 mm wire.
The second problem is the frame pulling out of square. A closed section is stiff in torsion, but a frame built from it bows under uneven heating just like any other. Tacks go closer than on a beam — every 200–300 mm — and welding alternates: opposite sides first, then the rest.
The third is moisture and rust inside. A closed section collects condensate, and a fully sealed frame bursts from pressure the first time it is heated hard if it has no vent. In hot-dip galvanised work vent holes are mandatory; in ordinary work they are simply sensible.
Cutting and fitting sections to each other is covered in welding hollow sections; matching current to thickness in the welding current calculator.
Frequently asked questions
How much does a 40×40×3 hollow section weigh?
3.30 kg per metre, so 19.8 kg over a 6 m length. A 40×40×2 weighs 2.31 kg/m and a 50×50×3 weighs 4.25 kg/m.
How much does a 42.4×3.2 tube weigh?
3.09 kg/m. The formula is short: mass per metre of tube is π · t · (D − t) · 7.85 / 1000, where D is the outside diameter and t the wall thickness, both in millimetres.
Why does the calculator overstate hollow section mass?
Because it takes the section as the difference of two rectangles and knows nothing about the corner radii. A real section has corners of roughly twice the wall thickness in radius, so there is less material there. The discrepancy is 3–7 % and grows with wall thickness. The tables below are worked out from the EN 10219 formula with the radii included — use those when the figure has to be exact.
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