Round Tube Sizes

Outside diameter, wall thickness, area and weight per foot for 25 HSS round tube and pipe-diameter sizes from 2 to 12.75 in, with metric equivalents.

Data verified 2026-09-29 · based on ASTM A500/A500M-23

HSS Round Tube Dimensions and Weight (ASTM A500)

Sizes below are given by outside diameter, which is how HSS round tube is specified. Several of the diameters listed — 2.375, 2.875, 4.000, 5.563, 6.625, 8.625, 10.75, 12.75 — are the standard pipe outside diameters, which is why the same nominal figures appear in both pipe and tube tables. They are not interchangeable: pipe is specified by nominal bore with a wall series (Schedule 40, 80 and so on), while tube is specified by outside diameter and wall thickness directly.

Weights are computed as A = π·t·(D − t), which reproduces published values to within 0.3% — round tube has no corner radii to correct for, which makes it the simplest of the three shapes to compute and the easiest to verify.

Round Tube vs Pipe

The two overlap in outside diameter and mean entirely different things.

Pipe is sized by nominal bore — the "2 inch pipe" in a schedule table has an outside diameter of 2.375 in, not 2.0, because the outside diameter is held constant and the wall thickness varies with the schedule. Its inside diameter therefore changes with the schedule while the outside stays the same, which is what allows the same fittings to work across schedules.

Tube is sized by outside diameter and wall thickness directly, so both are stated in the designation. Its inside diameter is whatever the two leave. This makes tube the right choice for structural and mechanical work, where the outside dimension is what fits the connection, and pipe the right choice for fluid conveyance, where the bore is what matters.

The practical trap is that a 2 in pipe and a 2 in round tube are not the same part and will not take the same fittings, even though the diagrams look alike. Check whether the drawing means nominal pipe size or outside diameter.

Frequently Asked Questions

Is round tube stronger than square tube?

Yes, for the same weight, in compression and torsion. A circle encloses the largest area for a given perimeter, so the material sits further from the centroid, and with no flat plate elements there is no local buckling to reduce the effective section. Square tube is chosen for connections, not for efficiency.

What is the difference between pipe and round tube?

Pipe is sized by nominal bore with a schedule wall series, so a 2 in pipe has a 2.375 in outside diameter. Tube is sized by outside diameter and wall thickness stated directly. The outside diameters overlap, which is what causes the confusion, but the fittings and the sizing basis are different.

How much does 4 inch round tube weigh?

10.0 lb/ft in a 1/4 in wall, 7.65 lb/ft in 3/16 in and 14.6 lb/ft in 3/8 in. Weight depends only on the diameter and the wall, computed as area = π × wall × (diameter − wall).

What does the D/t ratio mean?

Diameter divided by wall thickness — the slenderness of the tube wall. A low ratio means a compact, stocky tube that reaches yield before it buckles; a high ratio means a thin wall that buckles locally first. The AISC specification limits D/t by application and classifies sections accordingly.

Which is better for a column, round or square tube?

Round, on weight. A circular section has the same radius of gyration about every axis, so it never has a weak direction, and it resists local buckling better than a flat plate of the same thickness. Square is used where the column must connect to flat surfaces or where the shape matters architecturally.

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Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

Data Sources

Cross-checked against:

• Every weight recomputed from A = π·t·(D − t) at build time
• Four sizes held as known-value checks against published weights at 2% tolerance
• The pipe-coincident diameters checked against ASME B36.10M outside diameters
• Metric conversions recomputed for every row

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

Sizes are outside diameters and walls as specified for HSS round tube. Several diameters coincide with standard pipe outside diameters, but pipe is sized by nominal bore with a schedule wall series and the two are not interchangeable. Section properties are not given — take them from the AISC Shapes Database.

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