Gray Cast Iron Square Bar Weight
Mass per metre and per foot for gray cast iron square 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 27.0 kg (60.5 lb per 20 ft).
At the reference dimensions (a = 25 mm) this section has a cross-sectional area of 625.0 mm², giving 4.500 kg/m (3.024 lb/ft). Against carbon steel's 7,850 kg/m³ that is -8.3 % — the same section in steel would be 4.906 kg/m.
Square Bar — formula and derivation
Area of a square bar
A = a²
A = a², where a is the side length
Worked through with the default dimensions:
A = a²A = 25²A = 625.0 mm²
- a
- Side
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 4.5000 kg/m for the reference size above.
Cast iron square bar — size series
| Side | Cross-section | Mass / length |
|---|---|---|
| 6.0 mm | 36.00 mm² · 0.0558 in² | 0.259 kg/m · 0.174 lb/ft |
| 8.0 mm | 64.00 mm² · 0.0992 in² | 0.461 kg/m · 0.310 lb/ft |
| 10 mm | 100.00 mm² · 0.1550 in² | 0.720 kg/m · 0.484 lb/ft |
| 12 mm | 144.00 mm² · 0.2232 in² | 1.037 kg/m · 0.697 lb/ft |
| 16 mm | 256.00 mm² · 0.3968 in² | 1.843 kg/m · 1.239 lb/ft |
| 20 mm | 400.00 mm² · 0.6200 in² | 2.880 kg/m · 1.935 lb/ft |
| 25 mm | 625.00 mm² · 0.9688 in² | 4.500 kg/m · 3.024 lb/ft |
| 30 mm | 900.00 mm² · 1.3950 in² | 6.480 kg/m · 4.354 lb/ft |
| 40 mm | 1,600.00 mm² · 2.4800 in² | 11.520 kg/m · 7.741 lb/ft |
| 50 mm | 2,500.00 mm² · 3.8750 in² | 18.000 kg/m · 12.095 lb/ft |
| 60 mm | 3,600.00 mm² · 5.5800 in² | 25.920 kg/m · 17.417 lb/ft |
| 80 mm | 6,400.00 mm² · 9.9200 in² | 46.080 kg/m · 30.964 lb/ft |
| 100 mm | 10,000.00 mm² · 15.5000 in² | 72.000 kg/m · 48.382 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
Square 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 |
|---|---|---|---|
| 1/4 in | 6.35 | 40.32 mm² · 0.0625 in² | 0.290 kg/m · 0.195 lb/ft |
| 3/8 in | 9.52 | 90.73 mm² · 0.1406 in² | 0.653 kg/m · 0.439 lb/ft |
| 1/2 in | 12.70 | 161.29 mm² · 0.2500 in² | 1.161 kg/m · 0.780 lb/ft |
| 5/8 in | 15.88 | 252.02 mm² · 0.3906 in² | 1.815 kg/m · 1.219 lb/ft |
| 3/4 in | 19.05 | 362.90 mm² · 0.5625 in² | 2.613 kg/m · 1.756 lb/ft |
| 1 in | 25.40 | 645.16 mm² · 1.0000 in² | 4.645 kg/m · 3.121 lb/ft |
| 1-1/4 in | 31.75 | 1,008.06 mm² · 1.5625 in² | 7.258 kg/m · 4.877 lb/ft |
| 1-1/2 in | 38.10 | 1,451.61 mm² · 2.2500 in² | 10.452 kg/m · 7.023 lb/ft |
| 2 in | 50.80 | 2,580.64 mm² · 4.0000 in² | 18.581 kg/m · 12.486 lb/ft |
| 2-1/2 in | 63.50 | 4,032.25 mm² · 6.2500 in² | 29.032 kg/m · 19.509 lb/ft |
| 3 in | 76.20 | 5,806.44 mm² · 9.0000 in² | 41.806 kg/m · 28.093 lb/ft |
| 4 in | 101.60 | 10,322.56 mm² · 16.0000 in² | 74.322 kg/m · 49.942 lb/ft |
Stock sizes in inches, converted exactly at 25.4 mm per inch. Material: Gray Cast Iron at 7200 kg/m³.
The same square 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 | 4.906 | 3.297 | +0.0 % |
| Stainless Steel 304 | 8,000 | 0.2890 | 5.000 | 3.360 | +1.9 % |
| Stainless Steel 316 | 8,000 | 0.2890 | 5.000 | 3.360 | +1.9 % |
| Stainless Steel 316L | 8,000 | 0.2890 | 5.000 | 3.360 | +1.9 % |
| Stainless Steel 430 | 7,700 | 0.2782 | 4.813 | 3.234 | -1.9 % |
| Aluminum 6061-T6 | 2,700 | 0.0975 | 1.688 | 1.134 | -65.6 % |
| Aluminum 5052-H32 | 2,680 | 0.0968 | 1.675 | 1.126 | -65.9 % |
| Aluminum 7075-T6 | 2,810 | 0.1015 | 1.756 | 1.180 | -64.2 % |
| Copper C11000 | 8,940 | 0.3230 | 5.588 | 3.755 | +13.9 % |
| Brass C36000 | 8,500 | 0.3071 | 5.313 | 3.570 | +8.3 % |
| Bronze C93200 | 8,800 | 0.3179 | 5.500 | 3.696 | +12.1 % |
| Titanium Grade 2 | 4,510 | 0.1629 | 2.819 | 1.894 | -42.5 % |
| Gray Cast Iron | 7,200 | 0.2601 | 4.500 | 3.024 | -8.3 % |
| Lead | 11,340 | 0.4097 | 7.088 | 4.763 | +44.5 % |
| Rigid PVC (Type I) | 1,400 | 0.0506 | 0.875 | 0.588 | -82.2 % |
| HDPE (PE 100) | 960 | 0.0347 | 0.600 | 0.403 | -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 bar
A square bar has 27.3 % more area than the round bar that circumscribes it (a = d) and 21.5 % more mass — the corners of the square sit outside the circle. The reverse comparison is more useful in practice: a round bar of diameter d fits inside a square of side d with material to spare, so swapping square for round at the same nominal size removes about 21 % of the weight and produces a very similar-looking part.
Specified by side. State whether corners must be sharp or radiused; standard stock usually has a small corner radius.
Download this data
Cast iron square 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 square bar weigh?
At the reference dimensions (a = 25 mm) a gray cast iron square bar of this size weighs 4.500 kg/m, or 3.024 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 bar calculated?
Weight is cross-sectional area × length × density. For this shape the area is A = a². At the reference dimensions that gives 625.0 mm², and multiplying by gray cast iron's density of 7,200 kg/m³ gives 4.500 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 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 square 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 625.0 mm² (0.9688 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 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 square 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 4.906 kg/m for comparison.
Other materials, same square bar
The same geometry in every material, so the only variable is density.
- Carbon steel square bar — 7850 kg/m³
- SS 304 square bar — 8000 kg/m³
- SS 316 square bar — 8000 kg/m³
- AL 6061 square bar — 2700 kg/m³
- Copper square bar — 8940 kg/m³
- Brass square bar — 8500 kg/m³
- HDPE square bar — 960 kg/m³
- PVC square bar — 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 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
Square Bar area from A = a². 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.