MachineCalcs

Square Tube Weight Formula

Square tube weight is density times the hollow square area. For outside side a and wall t, the metal area is a^2 - (a - 2t)^2 before multiplying by length.

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Square tube formula

A square tube is an outside square minus an inside square. If a is outside side length and t is wall thickness, the inside side is a - 2t and the metal area is: A = a^2 - (a - 2t)^2 Then weight (kg) = rho * A * L / 1,000,000.

For weight per metre, use kg/m = rho * A / 1000. For mild steel, rho = 7.85 g/cm3.

Worked example: 50 x 50 x 3 steel tube

A 50 x 50 x 3 mm square steel tube has inside side 50 - 2 * 3 = 44 mm. Area is 50^2 - 44^2 = 564 mm2. Weight per metre is 7.85 * 564 / 1000 = 4.43 kg/m, so a 6 m length weighs about 26.6 kg.

Tube tolerances and corner radii

This formula treats the tube as a sharp-corner hollow square with uniform wall thickness. Real HSS and mechanical tubing have rounded corners, weld seams and mill tolerances, so supplier tables can differ slightly from the calculated value.

Square tube versus rectangular tube

Square tube uses one outside side dimension. Rectangular tube uses outside width, outside height and the same wall thickness subtraction on both dimensions. Use the rectangular tube calculator when the two outside sides are different.

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Last reviewed: June 1, 2026.