Steel weight & density
Structural steel has a density of about 7850 kg/m³ (0.284 lb/in³), so the weight of any steel bar, tube, angle or hollow section is its cross-sectional area times that density. The chart below lists common sizes with weight per metre and per foot; below it you can weigh any custom steel section from its geometry.
| Size | Shape | Area · mm² | Weight · kg/m | Weight · lb/ft |
|---|---|---|---|---|
| ⌀12 round bar | Round Rod | 113 | 0.888 | 0.597 |
| ⌀20 round bar | Round Rod | 314 | 2.466 | 1.657 |
| ⌀25 round bar | Round Rod | 491 | 3.853 | 2.589 |
| 50×6 flat bar | Flat Bar | 300 | 2.355 | 1.582 |
| 100×10 flat bar | Flat Bar | 1,000 | 7.850 | 5.275 |
| L 50×50×5 | Angle | 475 | 3.729 | 2.506 |
| L 100×100×10 | Angle | 1,900 | 14.915 | 10.022 |
| SHS 50×50×5 | Square Hollow | 900 | 7.065 | 4.747 |
| RHS 100×50×4 | Rectangular Hollow | 1,136 | 8.918 | 5.992 |
| CHS ⌀50×5 | Round Tube | 707 | 5.549 | 3.729 |
Computed from the exact section area × 7,850 kg/m³ (Structural steel S275 / A36). Fillets excluded (<2%). Verify against certified data before release.
DXF (LWPOLYLINE/CIRCLE) · CSV/XLSX with X,Y columns (blank row = new loop). DWG → export as DXF first.
EL 200,000 MPa · Structural steel S275 / A36
| Area | A | 5472 | mm² |
| Mass / metre | m | 42.955(28.865 lb/ft) | kg/m |
| 2nd moment | Ix | 4.754e+7 | mm⁴ |
| 2nd moment | Iy | 3.487e+6 | mm⁴ |
| Section mod. | Sx | 396173 | mm³ |
| Section mod. | Sy | 58118 | mm³ |
| Gyration | rx | 93.21 | mm |
| Gyration | ry | 25.24 | mm |
| Torsion | J | 262656 | mm⁴ |
| Published catalogue weight: 8.40 kg/m · computed Δ 411% | |||
Derived exactly from the section polygon (Green’s theorem). Fillets excluded (<2% effect). Verify against certified data before release.
The density of steel
Carbon and low-alloy structural steels (S275, S355, A36, A992) all sit very close to 7850 kg/m³ — 7.85 g/cm³, or 0.284 lb/in³. Small alloying changes move it only marginally, so 7850 is the standard figure used for weight take-offs. Cast iron is lighter (≈7200) and tool steels a little heavier, but for structural and general engineering steel, 7.85 is the number.
Weighing a steel section by hand
For a round bar, weight per metre ≈ 0.00617 × d² (d in mm) — a handy shop formula that is just π/4 × d² × 7850 × 10⁻⁶. A 20 mm bar is about 2.47 kg/m. For plate and flat bar, weight per m² ≈ 7.85 × thickness(mm). Dimviz does the exact integral for any shape so you never have to approximate a hollow or built-up section.
kg/m and lb/ft together
Steel is quoted in kg/m across most of the world and in lb/ft in North America. Because both come from the same area × density, the tool shows them side by side — switch to imperial and every section reports lb/ft, so a supplier quote in either unit is easy to check.
FAQ
What is the density of steel?+
About 7850 kg/m³, equal to 7.85 g/cm³ or 0.284 lb/in³ (490 lb/ft³) for carbon and low-alloy structural steel.
How do I calculate the weight of a steel bar?+
Weight per metre = cross-sectional area (m²) × 7850. For a round bar a quick formula is 0.00617 × diameter(mm)². Dimviz computes the area from any section and multiplies by density.
How much does a 20 mm steel round bar weigh?+
About 2.47 kg/m (1.66 lb/ft) — area π/4 × 20² = 314 mm², times 7850 kg/m³.