Gray Cast Iron Round Tube Weight
Mass per metre and per foot for gray cast iron round 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 19.1 kg (42.9 lb per 20 ft).
At the reference dimensions (D = 50 mm, t = 3 mm) this section has a cross-sectional area of 443.0 mm², giving 3.189 kg/m (2.143 lb/ft). Against carbon steel's 7,850 kg/m³ that is -8.3 % — the same section in steel would be 3.477 kg/m.
Round Tube — formula and derivation
Area of a round tube
A = π/4 · (D² − d²), d = D − 2t
A = π/4 × (D² − d²), where D is the outside diameter, d the inside diameter, and d = D − 2t for wall thickness t
Worked through with the default dimensions:
A = π/4 × (D² − d²)d = 50 − 2 × 3 = 44.0 mmA = 0.785398 × (50² − 44.0²)A = 0.785398 × 564.0A = 443.0 mm²
- D
- Outside diameter
- t
- Wall thickness — Must be less than half the outside diameter.
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 3.1893 kg/m for the reference size above.
Cast iron round tube — size series
| Outside diameter | 1.0 | 1.5 | 2.0 | 3.0 | 4.0 | 5.0 | 6.0 | 8.0 |
|---|---|---|---|---|---|---|---|---|
| 12 mm | 0.249 kg/m · 0.167 lb/ft | 0.356 kg/m · 0.239 lb/ft | 0.452 kg/m · 0.304 lb/ft | 0.611 kg/m · 0.410 lb/ft | 0.724 kg/m · 0.486 lb/ft | 0.792 kg/m · 0.532 lb/ft | 0.814 kg/m · 0.547 lb/ft | 0.724 kg/m · 0.486 lb/ft |
| 16 mm | 0.339 kg/m · 0.228 lb/ft | 0.492 kg/m · 0.331 lb/ft | 0.633 kg/m · 0.426 lb/ft | 0.882 kg/m · 0.593 lb/ft | 1.086 kg/m · 0.730 lb/ft | 1.244 kg/m · 0.836 lb/ft | 1.357 kg/m · 0.912 lb/ft | 1.448 kg/m · 0.973 lb/ft |
| 20 mm | 0.430 kg/m · 0.289 lb/ft | 0.628 kg/m · 0.422 lb/ft | 0.814 kg/m · 0.547 lb/ft | 1.154 kg/m · 0.775 lb/ft | 1.448 kg/m · 0.973 lb/ft | 1.696 kg/m · 1.140 lb/ft | 1.900 kg/m · 1.277 lb/ft | 2.171 kg/m · 1.459 lb/ft |
| 25 mm | 0.543 kg/m · 0.365 lb/ft | 0.797 kg/m · 0.536 lb/ft | 1.040 kg/m · 0.699 lb/ft | 1.493 kg/m · 1.003 lb/ft | 1.900 kg/m · 1.277 lb/ft | 2.262 kg/m · 1.520 lb/ft | 2.579 kg/m · 1.733 lb/ft | 3.076 kg/m · 2.067 lb/ft |
| 32 mm | 0.701 kg/m · 0.471 lb/ft | 1.035 kg/m · 0.695 lb/ft | 1.357 kg/m · 0.912 lb/ft | 1.968 kg/m · 1.322 lb/ft | 2.533 kg/m · 1.702 lb/ft | 3.054 kg/m · 2.052 lb/ft | 3.529 kg/m · 2.371 lb/ft | 4.343 kg/m · 2.918 lb/ft |
| 40 mm | 0.882 kg/m · 0.593 lb/ft | 1.306 kg/m · 0.878 lb/ft | 1.719 kg/m · 1.155 lb/ft | 2.511 kg/m · 1.687 lb/ft | 3.257 kg/m · 2.189 lb/ft | 3.958 kg/m · 2.660 lb/ft | 4.614 kg/m · 3.101 lb/ft | 5.791 kg/m · 3.891 lb/ft |
| 50 mm | 1.108 kg/m · 0.745 lb/ft | 1.646 kg/m · 1.106 lb/ft | 2.171 kg/m · 1.459 lb/ft | 3.189 kg/m · 2.143 lb/ft | 4.162 kg/m · 2.797 lb/ft | 5.089 kg/m · 3.420 lb/ft | 5.972 kg/m · 4.013 lb/ft | 7.600 kg/m · 5.107 lb/ft |
| 63 mm | 1.402 kg/m · 0.942 lb/ft | 2.087 kg/m · 1.402 lb/ft | 2.760 kg/m · 1.854 lb/ft | 4.072 kg/m · 2.736 lb/ft | 5.338 kg/m · 3.587 lb/ft | 6.560 kg/m · 4.408 lb/ft | 7.736 kg/m · 5.198 lb/ft | 9.953 kg/m · 6.688 lb/ft |
| 76 mm | 1.696 kg/m · 1.140 lb/ft | 2.528 kg/m · 1.699 lb/ft | 3.348 kg/m · 2.250 lb/ft | 4.954 kg/m · 3.329 lb/ft | 6.514 kg/m · 4.377 lb/ft | 8.030 kg/m · 5.396 lb/ft | 9.500 kg/m · 6.384 lb/ft | 12.305 kg/m · 8.269 lb/ft |
| 89 mm | 1.991 kg/m · 1.338 lb/ft | 2.969 kg/m · 1.995 lb/ft | 3.936 kg/m · 2.645 lb/ft | 5.836 kg/m · 3.921 lb/ft | 7.691 kg/m · 5.168 lb/ft | 9.500 kg/m · 6.384 lb/ft | 11.264 kg/m · 7.569 lb/ft | 14.657 kg/m · 9.849 lb/ft |
| 114 mm | 2.556 kg/m · 1.718 lb/ft | 3.817 kg/m · 2.565 lb/ft | 5.067 kg/m · 3.405 lb/ft | 7.532 kg/m · 5.061 lb/ft | 9.953 kg/m · 6.688 lb/ft | 12.328 kg/m · 8.284 lb/ft | 14.657 kg/m · 9.849 lb/ft | 19.181 kg/m · 12.889 lb/ft |
| 168 mm | 3.777 kg/m · 2.538 lb/ft | 5.649 kg/m · 3.796 lb/ft | 7.510 kg/m · 5.046 lb/ft | 11.197 kg/m · 7.524 lb/ft | 14.838 kg/m · 9.971 lb/ft | 18.435 kg/m · 12.388 lb/ft | 21.986 kg/m · 14.774 lb/ft | 28.953 kg/m · 19.455 lb/ft |
Rows: outside diameter (mm). Columns: wall thickness (mm). Computed for Gray Cast Iron at 7200 kg/m³.
| Outside diameter | 1.0 | 1.5 | 2.0 | 3.0 | 4.0 | 5.0 | 6.0 | 8.0 |
|---|---|---|---|---|---|---|---|---|
| 12 mm | 34.6 | 49.5 | 62.8 | 84.8 | 100.5 | 110.0 | 113.1 | 100.5 |
| 16 mm | 47.1 | 68.3 | 88.0 | 122.5 | 150.8 | 172.8 | 188.5 | 201.1 |
| 20 mm | 59.7 | 87.2 | 113.1 | 160.2 | 201.1 | 235.6 | 263.9 | 301.6 |
| 25 mm | 75.4 | 110.7 | 144.5 | 207.3 | 263.9 | 314.2 | 358.1 | 427.3 |
| 32 mm | 97.4 | 143.7 | 188.5 | 273.3 | 351.9 | 424.1 | 490.1 | 603.2 |
| 40 mm | 122.5 | 181.4 | 238.8 | 348.7 | 452.4 | 549.8 | 640.9 | 804.2 |
| 50 mm | 153.9 | 228.6 | 301.6 | 443.0 | 578.1 | 706.9 | 829.4 | 1,055.6 |
| 63 mm | 194.8 | 289.8 | 383.3 | 565.5 | 741.4 | 911.1 | 1,074.4 | 1,382.3 |
| 76 mm | 235.6 | 351.1 | 465.0 | 688.0 | 904.8 | 1,115.3 | 1,319.5 | 1,709.0 |
| 89 mm | 276.5 | 412.3 | 546.6 | 810.5 | 1,068.1 | 1,319.5 | 1,564.5 | 2,035.8 |
| 114 mm | 355.0 | 530.1 | 703.7 | 1,046.2 | 1,382.3 | 1,712.2 | 2,035.8 | 2,664.1 |
| 168 mm | 524.6 | 784.6 | 1,043.0 | 1,555.1 | 2,060.9 | 2,560.4 | 3,053.6 | 4,021.2 |
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 round 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 | 3.477 | 2.337 | +0.0 % |
| Stainless Steel 304 | 8,000 | 0.2890 | 3.544 | 2.381 | +1.9 % |
| Stainless Steel 316 | 8,000 | 0.2890 | 3.544 | 2.381 | +1.9 % |
| Stainless Steel 316L | 8,000 | 0.2890 | 3.544 | 2.381 | +1.9 % |
| Stainless Steel 430 | 7,700 | 0.2782 | 3.411 | 2.292 | -1.9 % |
| Aluminum 6061-T6 | 2,700 | 0.0975 | 1.196 | 0.804 | -65.6 % |
| Aluminum 5052-H32 | 2,680 | 0.0968 | 1.187 | 0.798 | -65.9 % |
| Aluminum 7075-T6 | 2,810 | 0.1015 | 1.245 | 0.836 | -64.2 % |
| Copper C11000 | 8,940 | 0.3230 | 3.960 | 2.661 | +13.9 % |
| Brass C36000 | 8,500 | 0.3071 | 3.765 | 2.530 | +8.3 % |
| Bronze C93200 | 8,800 | 0.3179 | 3.898 | 2.619 | +12.1 % |
| Titanium Grade 2 | 4,510 | 0.1629 | 1.998 | 1.342 | -42.5 % |
| Gray Cast Iron | 7,200 | 0.2601 | 3.189 | 2.143 | -8.3 % |
| Lead | 11,340 | 0.4097 | 5.023 | 3.375 | +44.5 % |
| Rigid PVC (Type I) | 1,400 | 0.0506 | 0.620 | 0.417 | -82.2 % |
| HDPE (PE 100) | 960 | 0.0347 | 0.425 | 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 round tube
Hollow sections are the most efficient way to buy stiffness by weight, and the numbers are stark: a 50 mm outside diameter tube with a 3 mm wall has the same area as a 22.6 mm solid bar — about 20 % of the mass — but its second moment of area is roughly 2.4 times larger. The catch is local: a thin wall buckles and dents long before it yields, so tube is chosen for stiffness and stability, never for where impact or crushing is expected.
Specified as outside diameter × wall thickness. State the standard (e.g. EN 10219) and whether the tube is welded or seamless.
Download this data
Cast iron round 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 round tube weigh?
At the reference dimensions (D = 50 mm, t = 3 mm) a gray cast iron round tube of this size weighs 3.189 kg/m, or 2.143 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 round tube calculated?
Weight is cross-sectional area × length × density. For this shape the area is A = π/4 · (D² − d²), d = D − 2t. At the reference dimensions that gives 443.0 mm², and multiplying by gray cast iron's density of 7,200 kg/m³ gives 3.189 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 round 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 round 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 443.0 mm² (0.6866 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 round 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 round 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 3.477 kg/m for comparison.
Other materials, same round tube
The same geometry in every material, so the only variable is density.
- Carbon steel round tube — 7850 kg/m³
- SS 304 round tube — 8000 kg/m³
- SS 316 round tube — 8000 kg/m³
- AL 6061 round tube — 2700 kg/m³
- Copper round tube — 8940 kg/m³
- Brass round tube — 8500 kg/m³
- HDPE round tube — 960 kg/m³
- PVC round 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 square tube — A = a² − (a − 2t)²
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
Round Tube area from A = π/4 · (D² − d²), d = D − 2t. 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.