Gray Cast Iron Round Bar Weight
Mass per metre and per foot for gray cast iron round bar 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 21.2 kg (47.5 lb per 20 ft).
At the reference dimensions (d = 25 mm) this section has a cross-sectional area of 490.9 mm², giving 3.534 kg/m (2.375 lb/ft). Against carbon steel's 7,850 kg/m³ that is -8.3 % — the same section in steel would be 3.853 kg/m.
Round Bar — formula and derivation
Area of a round bar
A = π/4 · d²
A = π/4 × d², where d is the outside diameter
Worked through with the default dimensions:
A = π/4 × d²A = 0.785398 × 25²A = 0.785398 × 625.0A = 490.9 mm²
- d
- Diameter — Outside diameter measured across the bar.
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 3.5343 kg/m for the reference size above.
Cast iron round bar — size series
| Diameter | Cross-section | Mass / length |
|---|---|---|
| 6.0 mm | 28.27 mm² · 0.0438 in² | 0.204 kg/m · 0.137 lb/ft |
| 8.0 mm | 50.27 mm² · 0.0779 in² | 0.362 kg/m · 0.243 lb/ft |
| 10 mm | 78.54 mm² · 0.1217 in² | 0.565 kg/m · 0.380 lb/ft |
| 12 mm | 113.10 mm² · 0.1753 in² | 0.814 kg/m · 0.547 lb/ft |
| 14 mm | 153.94 mm² · 0.2386 in² | 1.108 kg/m · 0.745 lb/ft |
| 16 mm | 201.06 mm² · 0.3116 in² | 1.448 kg/m · 0.973 lb/ft |
| 20 mm | 314.16 mm² · 0.4869 in² | 2.262 kg/m · 1.520 lb/ft |
| 25 mm | 490.87 mm² · 0.7609 in² | 3.534 kg/m · 2.375 lb/ft |
| 30 mm | 706.86 mm² · 1.0956 in² | 5.089 kg/m · 3.420 lb/ft |
| 32 mm | 804.25 mm² · 1.2466 in² | 5.791 kg/m · 3.891 lb/ft |
| 40 mm | 1,256.64 mm² · 1.9478 in² | 9.048 kg/m · 6.080 lb/ft |
| 50 mm | 1,963.50 mm² · 3.0434 in² | 14.137 kg/m · 9.500 lb/ft |
| 60 mm | 2,827.43 mm² · 4.3825 in² | 20.358 kg/m · 13.680 lb/ft |
| 80 mm | 5,026.55 mm² · 7.7912 in² | 36.191 kg/m · 24.319 lb/ft |
| 100 mm | 7,853.98 mm² · 12.1737 in² | 56.549 kg/m · 37.999 lb/ft |
Computed for Cast iron at 7200 kg/m³ (0.2601 lb/in³). ASTM A48 Class 30 / ISO 185.
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.
Imperial sizes
Round Bar is also bought in inch sizes. The conversions below are exact (1 in = 25.4 mm by definition), so the metric equivalents are the true millimetre dimensions rather than a rounded nominal figure.
| Stock size | Metric equivalent mm | Cross-section | Mass / length |
|---|---|---|---|
| 1/8 in | 3.17 | 7.92 mm² · 0.0123 in² | 0.057 kg/m · 0.038 lb/ft |
| 3/16 in | 4.76 | 17.81 mm² · 0.0276 in² | 0.128 kg/m · 0.086 lb/ft |
| 1/4 in | 6.35 | 31.67 mm² · 0.0491 in² | 0.228 kg/m · 0.153 lb/ft |
| 5/16 in | 7.94 | 49.48 mm² · 0.0767 in² | 0.356 kg/m · 0.239 lb/ft |
| 3/8 in | 9.52 | 71.26 mm² · 0.1104 in² | 0.513 kg/m · 0.345 lb/ft |
| 1/2 in | 12.70 | 126.68 mm² · 0.1963 in² | 0.912 kg/m · 0.613 lb/ft |
| 5/8 in | 15.88 | 197.93 mm² · 0.3068 in² | 1.425 kg/m · 0.958 lb/ft |
| 3/4 in | 19.05 | 285.02 mm² · 0.4418 in² | 2.052 kg/m · 1.379 lb/ft |
| 7/8 in | 22.22 | 387.95 mm² · 0.6013 in² | 2.793 kg/m · 1.877 lb/ft |
| 1 in | 25.40 | 506.71 mm² · 0.7854 in² | 3.648 kg/m · 2.452 lb/ft |
| 1-1/4 in | 31.75 | 791.73 mm² · 1.2272 in² | 5.700 kg/m · 3.831 lb/ft |
| 1-1/2 in | 38.10 | 1,140.09 mm² · 1.7671 in² | 8.209 kg/m · 5.516 lb/ft |
| 2 in | 50.80 | 2,026.83 mm² · 3.1416 in² | 14.593 kg/m · 9.806 lb/ft |
| 2-1/2 in | 63.50 | 3,166.92 mm² · 4.9087 in² | 22.802 kg/m · 15.322 lb/ft |
| 3 in | 76.20 | 4,560.37 mm² · 7.0686 in² | 32.835 kg/m · 22.064 lb/ft |
| 4 in | 101.60 | 8,107.32 mm² · 12.5664 in² | 58.373 kg/m · 39.225 lb/ft |
Stock sizes in inches, converted exactly at 25.4 mm per inch. Material: Gray Cast Iron at 7200 kg/m³.
The same round bar 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 | 3.853 | 2.589 | +0.0 % |
| Stainless Steel 304 | 8,000 | 0.2890 | 3.927 | 2.639 | +1.9 % |
| Stainless Steel 316 | 8,000 | 0.2890 | 3.927 | 2.639 | +1.9 % |
| Stainless Steel 316L | 8,000 | 0.2890 | 3.927 | 2.639 | +1.9 % |
| Stainless Steel 430 | 7,700 | 0.2782 | 3.780 | 2.540 | -1.9 % |
| Aluminum 6061-T6 | 2,700 | 0.0975 | 1.325 | 0.891 | -65.6 % |
| Aluminum 5052-H32 | 2,680 | 0.0968 | 1.316 | 0.884 | -65.9 % |
| Aluminum 7075-T6 | 2,810 | 0.1015 | 1.379 | 0.927 | -64.2 % |
| Copper C11000 | 8,940 | 0.3230 | 4.388 | 2.949 | +13.9 % |
| Brass C36000 | 8,500 | 0.3071 | 4.172 | 2.804 | +8.3 % |
| Bronze C93200 | 8,800 | 0.3179 | 4.320 | 2.903 | +12.1 % |
| Titanium Grade 2 | 4,510 | 0.1629 | 2.214 | 1.488 | -42.5 % |
| Gray Cast Iron | 7,200 | 0.2601 | 3.534 | 2.375 | -8.3 % |
| Lead | 11,340 | 0.4097 | 5.567 | 3.741 | +44.5 % |
| Rigid PVC (Type I) | 1,400 | 0.0506 | 0.687 | 0.462 | -82.2 % |
| HDPE (PE 100) | 960 | 0.0347 | 0.471 | 0.317 | -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 bar
Round bar is the only shape whose area grows with the square of a single dimension, so small diameter changes move weight much faster than intuition suggests: going from 25 mm to 28 mm — a 12 % diameter increase — raises the weight per metre by 25 %. This is why shaft stock is normally bought to the nearest preferred diameter rather than machined down from the next size up; the material saved is more than the weight table implies.
Specified by diameter only. For ground and polished stock, add the tolerance class and the straightness limit.
Download this data
Cast iron round bar — 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 bar weigh?
At the reference dimensions (d = 25 mm) a gray cast iron round bar of this size weighs 3.534 kg/m, or 2.375 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 bar calculated?
Weight is cross-sectional area × length × density. For this shape the area is A = π/4 · d². At the reference dimensions that gives 490.9 mm², and multiplying by gray cast iron's density of 7,200 kg/m³ gives 3.534 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 bar 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 bar?
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 490.9 mm² (0.7609 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 bar 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 bar 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 3.853 kg/m for comparison.
Other materials, same round bar
The same geometry in every material, so the only variable is density.
- Carbon steel round bar — 7850 kg/m³
- SS 304 round bar — 8000 kg/m³
- SS 316 round bar — 8000 kg/m³
- AL 6061 round bar — 2700 kg/m³
- Copper round bar — 8940 kg/m³
- Brass round bar — 8500 kg/m³
- HDPE round bar — 960 kg/m³
- PVC round bar — 1400 kg/m³
Other Cast iron sections
The same density applied to every shape the site covers.
- 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
- 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 Bar area from A = π/4 · d². 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.