Square tube is sold by weight but measured in metres — and that conversion is where money quietly disappears. Below is the chart we use for our own shipments, plus two quick ways to turn metres into tonnes.

Weight chart: square tube

Section, mm	Wall, mm	Weight per metre, kg	Metres per tonne
20×20	1.5	0.84	1190
25×25	1.5	1.07	935
30×30	2.0	1.68	595
40×40	2.0	2.30	435
40×40	3.0	3.33	300
50×50	3.0	4.27	234
60×60	3.0	5.21	192
80×80	4.0	9.22	108
100×100	4.0	11.73	85

Weight chart: rectangular tube

Section, mm	Wall, mm	Weight per metre, kg	Metres per tonne
40×20	2.0	1.68	595
50×25	2.0	2.15	465
60×40	2.0	2.93	341
60×40	3.0	4.27	234
80×40	3.0	5.21	192
100×50	3.0	6.62	151
120×60	4.0	10.47	96

How to calculate it yourself

Formula for a rectangular section: weight per metre = (2 × (A + B) − 4 × S) × S × 0.00785, where A and B are the sides in millimetres, S is the wall thickness and 0.00785 is the density of steel in g/mm³.

Example for 60×40×2: (2 × (60 + 40) − 4 × 2) × 2 × 0.00785 = 3.01 kg/m. The chart says 2.93 — the gap comes from the negative rolling tolerance, which is exactly why the actual batch weight always differs slightly from the calculated one.

The calculator on our home page does this automatically: pick a position, enter metres or tonnes, and you see the weight, the number of whole tubes and the total. Standard square tube length is 6 metres.

Why actual weight differs from the chart

Chart weights are nominal. Real weight varies by 2–5% because of the wall thickness tolerance. A tube on the negative side of the tolerance is lighter, so the same tonne gives you more metres — but it also carries less load. That matters for structural work; for fences and canopies it effectively does not.