Carbon Steel Square Tube Weight
Mass per metre and per foot for carbon steel square tube at 7,850 kg/m³ (ASTM A36 / AISI 1018 / EN 10025 S275). Every figure is for the section as drawn. A 6 m length of this size weighs 20.9 kg (46.8 lb per 20 ft).
At the reference dimensions (a = 40 mm, t = 3 mm) this section has a cross-sectional area of 444.0 mm², giving 3.485 kg/m (2.342 lb/ft). This is the baseline density, so the figures here are what a steel weight chart shows.
Square Tube — formula and derivation
Area of a square tube
A = a² − (a − 2t)²
A = a² − (a − 2t)², which expands to A = 4t(a − t)
Worked through with the default dimensions:
A = a² − (a − 2t)²Inner side = 40 − 2 × 3 = 34.0 mmA = 40² − 34.0²A = 1600.0 − 1156.0A = 444.0 mm²
- a
- Side
- t
- Wall thickness
Weight follows from the area with no further geometry: m = A × 10⁻⁶ × ρ, where A is in mm², ρ in kg/m³ and m in kg/m. At 7,850 kg/m³ that is 3.4854 kg/m for the reference size above.
Carbon steel square tube — size series
| Side | 1.5 | 2.0 | 3.0 | 4.0 | 5.0 | 6.0 |
|---|---|---|---|---|---|---|
| 15 mm | 0.636 kg/m · 0.427 lb/ft | 0.816 kg/m · 0.549 lb/ft | 1.130 kg/m · 0.760 lb/ft | 1.382 kg/m · 0.928 lb/ft | 1.570 kg/m · 1.055 lb/ft | 1.696 kg/m · 1.139 lb/ft |
| 20 mm | 0.871 kg/m · 0.586 lb/ft | 1.130 kg/m · 0.760 lb/ft | 1.601 kg/m · 1.076 lb/ft | 2.010 kg/m · 1.350 lb/ft | 2.355 kg/m · 1.582 lb/ft | 2.638 kg/m · 1.772 lb/ft |
| 25 mm | 1.107 kg/m · 0.744 lb/ft | 1.444 kg/m · 0.971 lb/ft | 2.072 kg/m · 1.393 lb/ft | 2.638 kg/m · 1.772 lb/ft | 3.140 kg/m · 2.110 lb/ft | 3.580 kg/m · 2.405 lb/ft |
| 30 mm | 1.342 kg/m · 0.902 lb/ft | 1.758 kg/m · 1.182 lb/ft | 2.543 kg/m · 1.709 lb/ft | 3.266 kg/m · 2.194 lb/ft | 3.925 kg/m · 2.637 lb/ft | 4.522 kg/m · 3.038 lb/ft |
| 40 mm | 1.813 kg/m · 1.219 lb/ft | 2.386 kg/m · 1.604 lb/ft | 3.485 kg/m · 2.342 lb/ft | 4.522 kg/m · 3.038 lb/ft | 5.495 kg/m · 3.692 lb/ft | 6.406 kg/m · 4.304 lb/ft |
| 50 mm | 2.284 kg/m · 1.535 lb/ft | 3.014 kg/m · 2.026 lb/ft | 4.427 kg/m · 2.975 lb/ft | 5.778 kg/m · 3.882 lb/ft | 7.065 kg/m · 4.747 lb/ft | 8.290 kg/m · 5.570 lb/ft |
| 60 mm | 2.755 kg/m · 1.852 lb/ft | 3.642 kg/m · 2.448 lb/ft | 5.369 kg/m · 3.608 lb/ft | 7.034 kg/m · 4.726 lb/ft | 8.635 kg/m · 5.802 lb/ft | 10.174 kg/m · 6.836 lb/ft |
| 80 mm | 3.697 kg/m · 2.485 lb/ft | 4.898 kg/m · 3.292 lb/ft | 7.253 kg/m · 4.874 lb/ft | 9.546 kg/m · 6.414 lb/ft | 11.775 kg/m · 7.912 lb/ft | 13.942 kg/m · 9.368 lb/ft |
| 100 mm | 4.639 kg/m · 3.117 lb/ft | 6.154 kg/m · 4.136 lb/ft | 9.137 kg/m · 6.140 lb/ft | 12.058 kg/m · 8.102 lb/ft | 14.915 kg/m · 10.022 lb/ft | 17.710 kg/m · 11.900 lb/ft |
Rows: side (mm). Columns: wall thickness (mm). Computed for Carbon Steel at 7850 kg/m³.
| Side | 1.5 | 2.0 | 3.0 | 4.0 | 5.0 | 6.0 |
|---|---|---|---|---|---|---|
| 15 mm | 81.0 | 104.0 | 144.0 | 176.0 | 200.0 | 216.0 |
| 20 mm | 111.0 | 144.0 | 204.0 | 256.0 | 300.0 | 336.0 |
| 25 mm | 141.0 | 184.0 | 264.0 | 336.0 | 400.0 | 456.0 |
| 30 mm | 171.0 | 224.0 | 324.0 | 416.0 | 500.0 | 576.0 |
| 40 mm | 231.0 | 304.0 | 444.0 | 576.0 | 700.0 | 816.0 |
| 50 mm | 291.0 | 384.0 | 564.0 | 736.0 | 900.0 | 1,056.0 |
| 60 mm | 351.0 | 464.0 | 684.0 | 896.0 | 1,100.0 | 1,296.0 |
| 80 mm | 471.0 | 624.0 | 924.0 | 1,216.0 | 1,500.0 | 1,776.0 |
| 100 mm | 591.0 | 784.0 | 1,164.0 | 1,536.0 | 1,900.0 | 2,256.0 |
Area is a property of the geometry alone, so this table is the same for every material. It is what you enter into a stress calculation; the mass table is what you enter into an order.
Each row is one nominal size. Because the area is computed from your dimensions rather than read from a mill table, a non-standard size is just as accurate — put it into the calculator above rather than interpolating between rows.
The same square tube in every material
Geometry is fixed and only density changes, so this table is the whole material-selection question in one view. Carbon Steel is highlighted. The percentage column is against carbon steel, which is the figure most quotations are built on.
| Material | Density kg/m³ | lb/in³ | Mass / length kg/m | lb/ft | vs carbon steel |
|---|---|---|---|---|---|
| Carbon Steel | 7,850 | 0.2836 | 3.485 | 2.342 | +0.0 % |
| Stainless Steel 304 | 8,000 | 0.2890 | 3.552 | 2.387 | +1.9 % |
| Stainless Steel 316 | 8,000 | 0.2890 | 3.552 | 2.387 | +1.9 % |
| Stainless Steel 316L | 8,000 | 0.2890 | 3.552 | 2.387 | +1.9 % |
| Stainless Steel 430 | 7,700 | 0.2782 | 3.419 | 2.297 | -1.9 % |
| Aluminum 6061-T6 | 2,700 | 0.0975 | 1.199 | 0.806 | -65.6 % |
| Aluminum 5052-H32 | 2,680 | 0.0968 | 1.190 | 0.800 | -65.9 % |
| Aluminum 7075-T6 | 2,810 | 0.1015 | 1.248 | 0.838 | -64.2 % |
| Copper C11000 | 8,940 | 0.3230 | 3.969 | 2.667 | +13.9 % |
| Brass C36000 | 8,500 | 0.3071 | 3.774 | 2.536 | +8.3 % |
| Bronze C93200 | 8,800 | 0.3179 | 3.907 | 2.626 | +12.1 % |
| Titanium Grade 2 | 4,510 | 0.1629 | 2.002 | 1.346 | -42.5 % |
| Gray Cast Iron | 7,200 | 0.2601 | 3.197 | 2.148 | -8.3 % |
| Lead | 11,340 | 0.4097 | 5.035 | 3.383 | +44.5 % |
| Rigid PVC (Type I) | 1,400 | 0.0506 | 0.622 | 0.418 | -82.2 % |
| HDPE (PE 100) | 960 | 0.0347 | 0.426 | 0.286 | -87.8 % |
Same geometry throughout, so the only variable is density. Carbon steel is highlighted as the baseline.
A note on using this table for costing: mass is not price. Aluminium is roughly a third of steel's mass here, but per kilogram it costs several times more, so a straight swap rarely saves money — what it buys is reduced load on a structure or a vehicle.
About carbon steel
The baseline against which every other metal is compared. Mild and medium carbon steels sit at 7,850 kg/m³ across the usual structural and free-machining grades: A36 plate, 1018 shaft, S275JR section. Carbon content moves density so little over the 0.05–0.60 % range that one figure covers the family, which is why mill weight tables for "steel" almost always assume 7,850 kg/m³ (0.2836 lb/in³). Use this entry when the drawing says "steel" and no grade is called out.
- Density
- 7,850 kg/m³ = 0.2836 lb/in³ · 1.0000× carbon steel · typical spread ±1 %
- Specification
- ASTM A36 / AISI 1018 / EN 10025 S275
- Equivalents
- AISI 1018 · EN 1.0401 · JIS SS400 · GB Q235
- Typical uses
- Structural sections · Plate and bar stock · Fabricated weldments · Shafts and pins
Unprotected carbon steel corrodes at roughly 0.1 mm/year in a mild inland atmosphere and far faster in coastal or chemical service, so a corrosion allowance changes the mass you should order — not this density.
About square tube
Square tube expands cleanly to A = 4t(a − t), which makes the sensitivity obvious: for a given side, weight is almost exactly linear in wall thickness. Doubling a 2 mm wall to 4 mm adds about 1.9 times the mass, not twice, because the inner void shrinks as the wall grows. Its flat faces also make it the natural choice for welded frames and for anything that has to be drilled, tapped or bolted through a face — a round tube gives you only a tangent point where a square tube gives you a full flat.
Specified as side × wall thickness. Corner radii are standardised per EN 10219 and change the area slightly at heavier walls.
Download this data
Carbon steel square tube — CSV
Both buttons below read the tables rendered on this page, so the file matches what you are looking at. The full catalogue — all 16 materials across all 10 sections — is on the downloads page.
Fields are quoted per RFC 4180, with a UTF-8 byte-order mark so Excel reads the mm² and · characters correctly. Blank lines separate the weight matrix from the area matrix.
Frequently asked questions
How much does carbon steel square tube weigh?
At the reference dimensions (a = 40 mm, t = 3 mm) a carbon steel square tube of this size weighs 3.485 kg/m, or 2.342 lb/ft. The table above lists the figure for every standard size so you can read your size directly instead of scaling.
How is the weight of square tube calculated?
Weight is cross-sectional area × length × density. For this shape the area is A = a² − (a − 2t)². At the reference dimensions that gives 444.0 mm², and multiplying by carbon steel's density of 7,850 kg/m³ gives 3.485 kg/m. Nothing is looked up in a table — which is why a non-standard size is calculated just as accurately as a standard one.
Why does carbon steel weigh more or less than steel?
It is the 7,850 kg/m³ baseline that every other figure on this site is measured against. Density is the only variable: the cross-sectional area depends purely on geometry, so a square tube of the same dimensions has the same area in every material and the mass simply scales with density. In this case the ratio is 1.0000× carbon steel.
What is the cross-sectional area of a square tube?
The area depends only on the dimensions, not on the material, so it is identical whichever material you select: at the reference dimensions it is 444.0 mm² (0.6882 in²). That is the number you would enter into a stress or deflection calculation, and it is why changing material on this page never changes the area column.
Does a carbon steel square tube weigh the same as a carbon steel part of a different shape?
No, and the difference is larger than most people expect. At equal nominal size, a square bar is 27.3 % heavier than a round bar, and a hollow section is typically 60–80 % lighter than the solid bar it replaces. Weight follows area, and area changes faster than dimensions do — which is exactly why this needs calculating rather than estimating.
Other materials, same square tube
The same geometry in every material, so the only variable is density.
- SS 304 square tube — 8000 kg/m³
- SS 316 square tube — 8000 kg/m³
- AL 6061 square tube — 2700 kg/m³
- Copper square tube — 8940 kg/m³
- Brass square tube — 8500 kg/m³
- HDPE square tube — 960 kg/m³
- PVC square tube — 1400 kg/m³
- AL 5052 square tube — 2680 kg/m³
Other Carbon steel sections
The same density applied to every shape the site covers.
- Carbon steel round bar — A = π/4 · d²
- Carbon steel square bar — A = a²
- Carbon steel hexagonal bar — A = (√3/2) · AF² ≈ 0.8660 · AF²
- Carbon steel flat bar — A = w · t
- Carbon steel plate — A = w · t
- Carbon steel round tube — A = π/4 · (D² − d²), d = D − 2t
Reference data and tools
- Metal weight overview — how the calculation works
- All 16 materials — densities and specifications
- All 10 sections — formulas and size series
- Density chart — lightest to heaviest
- Metal weight calculator — any size, any material
- All calculators — metal weight and pipe weight
- Download the data — CSV, generated from the same source
- Cross-reference tables — DN / NPS / material equivalents
- Methodology and sources — where every number comes from
Square Tube area from A = a² − (a − 2t)². Mass computed as area × length × density at 7,850 kg/m³ (ASTM A36 / AISI 1018 / EN 10025 S275). No weight on this page is copied from a published table — which is why figures can differ in the last significant digit from a mill's chart calculated at a nominal density.
- Elementary plane geometry. The circle, polygon and hollow-section area formulas.
- ASTM material specifications for each grade named in the material entry (A36, A240/A276, B209/B211/B221, B152/B16/B505, B265/B348, A48, B29, D1784, D3350).
- BIPM / NIST definitional constants: international inch = 25.4 mm, foot = 0.3048 m, pound = 0.45359237 kg.
Dataset version 2026.09.1 · dimensions last verified against source 2026-09-21. Found an error? Report it — corrections are issued with a version bump.