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.

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.

Page last changed 2026-10-19 · based on ASTM A500/A500M-23

Find a size

HSS Round Tube Dimensions and Weight (ASTM A500)

Size^[1]	Outside dia in^[1]	Wall in^[1]	Area in²^[3]	Weight lb/ft^[3]	Weight kg/m^[3]	Outside dia mm^[2]	Wall mm^[2]	D/t ratio^[3]
HSS2.000×0.125 #	2.000	0.125	0.736	2.51	3.73	50.8	3.17	16.0
HSS2.000×0.188 #	2.000	0.188	1.070	3.64	5.42	50.8	4.78	10.6
HSS2.375×0.154 #	2.375	0.154	1.075	3.66	5.44	60.3	3.91	15.4
HSS2.500×0.188 #	2.500	0.188	1.366	4.65	6.92	63.5	4.78	13.3
HSS2.875×0.203 #	2.875	0.203	1.704	5.80	8.63	73.0	5.16	14.2
HSS3.000×0.188 #	3.000	0.188	1.661	5.65	8.41	76.2	4.78	16.0
HSS3.000×0.25 #	3.000	0.25	2.160	7.35	10.94	76.2	6.35	12.0
HSS3.500×0.188 #	3.500	0.188	1.956	6.66	9.91	88.9	4.78	18.6
HSS3.500×0.25 #	3.500	0.25	2.553	8.69	12.93	88.9	6.35	14.0
HSS4.000×0.188 #	4.000	0.188	2.251	7.66	11.40	101.6	4.78	21.3
HSS4.000×0.25 #	4.000	0.25	2.945	10.02	14.92	101.6	6.35	16.0
HSS4.000×0.375 #	4.000	0.375	4.271	14.53	21.63	101.6	9.52	10.7
HSS5.000×0.25 #	5.000	0.25	3.731	12.70	18.89	127.0	6.35	20.0
HSS5.000×0.375 #	5.000	0.375	5.449	18.54	27.59	127.0	9.52	13.3
HSS5.563×0.258 #	5.563	0.258	4.300	14.63	21.78	141.3	6.55	21.6
HSS6.000×0.25 #	6.000	0.25	4.516	15.37	22.87	152.4	6.35	24.0
HSS6.000×0.375 #	6.000	0.375	6.627	22.55	33.56	152.4	9.52	16.0
HSS6.625×0.28 #	6.625	0.28	5.581	18.99	28.27	168.3	7.11	23.7
HSS8.000×0.25 #	8.000	0.25	6.087	20.71	30.83	203.2	6.35	32.0
HSS8.000×0.375 #	8.000	0.375	8.983	30.57	45.49	203.2	9.52	21.3
HSS8.625×0.322 #	8.625	0.322	8.399	28.58	42.54	219.1	8.18	26.8
HSS10.000×0.375 #	10.000	0.375	11.339	38.59	57.43	254.0	9.52	26.7
HSS10.750×0.365 #	10.750	0.365	11.908	40.53	60.31	273.1	9.27	29.5
HSS12.000×0.375 #	12.000	0.375	13.695	46.61	69.36	304.8	9.52	32.0
HSS12.750×0.375 #	12.750	0.375	14.579	49.62	73.84	323.8	9.52	34.0

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.

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.

#	Source	Type	Revision / method
[1]	ASTM A500 — Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes	reference	ASTM A500/A500M-23
[2]	Section area and weight computed from the section geometry	derived	Computed at build time from the closed-form area formula for the section shape, multiplied by 12 in/ft and the steel density 0.2836 lb/in³. Every row is verified against a published weight held as a known-value check at 1% tolerance, so an error in either the geometry or the formula fails the build.
[3]	Section area and weight computed from the section geometry	derived	Computed at build time from the closed-form area formula for the section shape, multiplied by 12 in/ft and the steel density 0.2836 lb/in³. Every row is verified against a published weight held as a known-value check at 1% tolerance, so an error in either the geometry or the formula fails the build.

Data Sources

Standard	Revision	What it covers on this page
ASTM A500 — Cold-Formed Welded and Seamless Carbon Steel Structural Tubing	ASTM A500/A500M-23	the round tube outside diameters and wall thicknesses
ASME B36.10M — Welded and Seamless Wrought Steel Pipe	ASME B36.10M-2018	the pipe outside diameters that coincide with several sizes listed
AISC Steel Construction Manual, Shapes Database	AISC 15th edition (2017)	the published weights used as anchors

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:

Value	How it is derived
Area and weight	A = π·t·(D − t), exact for a circular tube with sharp edges (round tube has no corner radii to correct). Weight = A × 12 × 0.2836. Verified against published weights at build time.
Metric dimensions	Inches × 25.4, recomputed at build time.

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.

Accuracy and use. Use the source notes and recorded verification scope above to assess each value. Calculated values follow the stated derivations; compilation values may lack a confirmed original document or product condition. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

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Read the source notes, calculation methods and verification scope above before reusing a value. To cite this page:

Plain text

Engineering Reference. "Round Tube Sizes." https://refmanual.com/charts/round-tube-sizes/ (accessed 2026-10-19). Data from ASTM A500 — Cold-Formed Welded and Seamless Carbon Steel Structural Tubing, ASTM A500/A500M-23.

BibTeX

@misc{round-tube-sizes,
  title        = {Round Tube Sizes},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/round-tube-sizes/}},
  note         = {Accessed: 2026-10-19},
  source       = {ASTM A500 — Cold-Formed Welded and Seamless Carbon Steel Structural Tubing, ASTM A500/A500M-23}
}

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TY  - ELEC
TI  - Round Tube Sizes
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/round-tube-sizes/
PY  - 2026
DA  - 2026-10-19
N1  - Source: ASTM A500 — Cold-Formed Welded and Seamless Carbon Steel Structural Tubing, ASTM A500/A500M-23
ER  -

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