Gray Cast Iron Square Tube Weight
Mass per metre and per foot for gray cast iron square tube at 7,200 kg/m³ (ASTM A48 Class 30 / ISO 185). Every figure is for the section as drawn. A 6 m length of this size weighs 19.2 kg (43.0 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 3.197 kg/m (2.148 lb/ft). Against carbon steel's 7,850 kg/m³ that is -8.3 % — the same section in steel would be 3.485 kg/m.
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 7,200 kg/m³ that is 3.1968 kg/m for the reference size above.
Cast iron square tube — size series
| Side | 1.5 | 2.0 | 3.0 | 4.0 | 5.0 | 6.0 |
|---|---|---|---|---|---|---|
| 15 mm | 0.583 kg/m · 0.392 lb/ft | 0.749 kg/m · 0.503 lb/ft | 1.037 kg/m · 0.697 lb/ft | 1.267 kg/m · 0.852 lb/ft | 1.440 kg/m · 0.968 lb/ft | 1.555 kg/m · 1.045 lb/ft |
| 20 mm | 0.799 kg/m · 0.537 lb/ft | 1.037 kg/m · 0.697 lb/ft | 1.469 kg/m · 0.987 lb/ft | 1.843 kg/m · 1.239 lb/ft | 2.160 kg/m · 1.451 lb/ft | 2.419 kg/m · 1.626 lb/ft |
| 25 mm | 1.015 kg/m · 0.682 lb/ft | 1.325 kg/m · 0.890 lb/ft | 1.901 kg/m · 1.277 lb/ft | 2.419 kg/m · 1.626 lb/ft | 2.880 kg/m · 1.935 lb/ft | 3.283 kg/m · 2.206 lb/ft |
| 30 mm | 1.231 kg/m · 0.827 lb/ft | 1.613 kg/m · 1.084 lb/ft | 2.333 kg/m · 1.568 lb/ft | 2.995 kg/m · 2.013 lb/ft | 3.600 kg/m · 2.419 lb/ft | 4.147 kg/m · 2.787 lb/ft |
| 40 mm | 1.663 kg/m · 1.118 lb/ft | 2.189 kg/m · 1.471 lb/ft | 3.197 kg/m · 2.148 lb/ft | 4.147 kg/m · 2.787 lb/ft | 5.040 kg/m · 3.387 lb/ft | 5.875 kg/m · 3.948 lb/ft |
| 50 mm | 2.095 kg/m · 1.408 lb/ft | 2.765 kg/m · 1.858 lb/ft | 4.061 kg/m · 2.729 lb/ft | 5.299 kg/m · 3.561 lb/ft | 6.480 kg/m · 4.354 lb/ft | 7.603 kg/m · 5.109 lb/ft |
| 60 mm | 2.527 kg/m · 1.698 lb/ft | 3.341 kg/m · 2.245 lb/ft | 4.925 kg/m · 3.309 lb/ft | 6.451 kg/m · 4.335 lb/ft | 7.920 kg/m · 5.322 lb/ft | 9.331 kg/m · 6.270 lb/ft |
| 80 mm | 3.391 kg/m · 2.279 lb/ft | 4.493 kg/m · 3.019 lb/ft | 6.653 kg/m · 4.470 lb/ft | 8.755 kg/m · 5.883 lb/ft | 10.800 kg/m · 7.257 lb/ft | 12.787 kg/m · 8.593 lb/ft |
| 100 mm | 4.255 kg/m · 2.859 lb/ft | 5.645 kg/m · 3.793 lb/ft | 8.381 kg/m · 5.632 lb/ft | 11.059 kg/m · 7.431 lb/ft | 13.680 kg/m · 9.193 lb/ft | 16.243 kg/m · 10.915 lb/ft |
Rows: side (mm). Columns: wall thickness (mm). Computed for Gray Cast Iron at 7200 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. Gray Cast Iron 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 gray cast iron
The only common ferrous material lighter than steel, because the graphite flakes that give cast iron its damping and machinability also displace iron — 7,200 kg/m³ against steel’s 7,850, an 8.3 % saving. Those flakes are also why it fails in tension but excels in compression, and why engine blocks, machine bases and drainage products are cast iron. Normal spread is 7,150–7,350 kg/m³, so a large casting should always be weighed against the foundry’s own figure.
- Density
- 7,200 kg/m³ = 0.2601 lb/in³ · 0.9172× carbon steel · typical spread ±3 %
- Specification
- ASTM A48 Class 30 / ISO 185
- Equivalents
- EN GJL-250 · JIS FC250 · GB HT250
- Typical uses
- Machine tool bases · Engine blocks and manifolds · Drainage and soil pipe · Column and bracket castings
Density varies with graphite content and section thickness — thin sections cool faster and can differ from a heavy boss in the same casting.
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
Cast iron 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 gray cast iron square tube weigh?
At the reference dimensions (a = 40 mm, t = 3 mm) a gray cast iron square tube of this size weighs 3.197 kg/m, or 2.148 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 gray cast iron's density of 7,200 kg/m³ gives 3.197 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 gray cast iron weigh more or less than steel?
It is lighter than carbon steel for the same section — about 8 % lighter at 7,200 kg/m³. 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 0.9172× 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 cast iron square tube weigh the same as a cast iron 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.
Should I use Cast iron weight or carbon steel weight for costing?
Use the material you are actually buying. At 7,200 kg/m³ against carbon steel's 7,850 kg/m³, the same square tube differs by 8.3 % in mass. On a per-metre quote that is invisible; on a fabricated tonnage it is the difference between a margin and a loss. This page computes the steel figure as 3.485 kg/m for comparison.
Other materials, same square tube
The same geometry in every material, so the only variable is density.
- Carbon steel square tube — 7850 kg/m³
- 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
Other Cast iron sections
The same density applied to every shape the site covers.
- Cast iron round bar — A = π/4 · d²
- Cast iron square bar — A = a²
- Cast iron hexagonal bar — A = (√3/2) · AF² ≈ 0.8660 · AF²
- Cast iron flat bar — A = w · t
- Cast iron plate — A = w · t
- Cast iron 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 7,200 kg/m³ (ASTM A48 Class 30 / ISO 185). 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.