Square Tube Sizes

HSS Square Tube Dimensions and Weight (ASTM A500)

Size is written as outside dimension × outside dimension × wall thickness, so HSS4×4×1/4 is 4 in square with a 1/4 in wall — not a 4 in bore. Wall thickness is what sets the strength and the weight, and the two are independent choices: HSS4×4 is stocked in walls from 1/8 to 1/2 in, a weight range of 6 to 19 lb/ft for the same outside dimension.

Weights are computed from the section geometry using the A500 corner radii (outside radius = 2t, inside radius = t) and verified against published values on every row. The t/b ratio column is the wall-to-width ratio that governs local buckling — the lower it is, the more the tube behaves as a thin-walled section rather than a solid.

Wall Thickness Classes and the t/b Ratio

A500 tubing is made in three wall classes — 5% (thin), 10% (standard) and 15% — named for the ratio of wall thickness to the outside dimension. A 4 in square tube in the 10% class has a wall around 0.25 in. The ratio matters because it governs local buckling: a thin wall buckles at a lower stress than a thick one, so a slender tube reaches its limit by local crippling rather than by yielding or overall column buckling.

The practical consequence is that strength does not scale with area alone. A 6×6×0.25 tube has more area than a 4×4×0.375, but its lower t/b ratio means its walls buckle earlier — which is why the section property tables give effective widths for slender sections rather than the full gross section.

Round tube is the exception: with no flat plate elements there is no local buckling in the same sense, which is why round HSS is the most efficient shape for a given weight in compression and torsion. Square and rectangular tube exist because they are far easier to connect and to clad.

Why the Corner Radii Matter to the Weight

A500 requires rounded outside corners with a radius of twice the wall thickness. Those corners remove material relative to a sharp-cornered box — about 4 to 5% of the area for a square tube — and a weight computed from sharp corners will be that much too high.

That is why the weights on this page are computed with A = 4t(b − t) − (4 − π)·3t² rather than the simpler 4t(b − t). The difference is small in absolute terms and consistent in sign, so a table built on the sharp-corner formula would be systematically heavy on every row — the kind of error that shows up as an overstated shipping weight rather than as an obvious mistake.

Structural plate and beam weights do not have this issue, because their designations carry the nominal weight directly. Tube is the case where the weight has to be computed, and therefore the case where the corner geometry has to be right.

Frequently Asked Questions

How do I read a square tube size?

As outside dimension × outside dimension × wall thickness. HSS4×4×1/4 is 4 in square on the outside with a 1/4 in wall, giving a 3.5 in inside dimension. The size is never the bore — a 4 in square tube has a 3.5 in opening in the standard 1/4 in wall.

How much does square tube weigh?

It depends on both the size and the wall. HSS4×4 weighs 6.9 lb/ft in a 1/8 in wall, 12.2 lb/ft in 1/4 in and 19.0 lb/ft in 3/8 in. The table above gives the weight for each combination, computed from the section geometry and checked against published values.

What does the t/b ratio mean?

The wall thickness divided by the outside dimension, which governs local buckling. A low ratio means a thin wall that can buckle before the section yields, so the section's effective strength is lower than its gross area suggests. A500 tube is classified by this ratio into 5%, 10% and 15% wall classes.

Is square tube stronger than round?

No — for the same weight, round tube is stronger in compression and torsion because it has no flat plate elements to buckle locally and its material sits further from the centroid. Square tube is used because it is far easier to connect, to clad and to fit into a rectangular frame.

What is the difference between HSS and pipe?

HSS is sized by its outside dimension, pipe by its nominal bore. A 4 in square HSS is 4 in across the outside; a 4 in pipe has an outside diameter of about 4.5 in. The two are specified on completely different bases and their wall thickness series do not correspond.

Related

• Rectangular Tube Sizes
• Round Tube Sizes
• Steel Beam Sizes
• Steel Plate Sizes
• Section Modulus Calculator

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

Data Sources

Verification scope

No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.

Derived values — the following values on this page are calculated, not taken directly from the standard:

Weights are computed from nominal geometry at the standard steel density. Delivered tube is within the A500 wall tolerance, which is a percentage of the nominal wall, so actual weight varies by a few percent. Section properties — I, S, r — are not given and should come from the AISC Shapes Database, since they depend on the corner radii and the effective width of slender elements.

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