How to calculate or look up steel-section unit weight

For a standard rolled section such as HEA, HEB, IPE, UPN, UB or UC, the best answer to “what is the kg/m?” is usually:

look it up in the current section table.

The reason is simple: rolled sections contain root fillets and exact mill geometry that are not captured perfectly by a quick rectangle formula.

For non-standard or fabricated sections, unit weight can be calculated from cross-sectional area.

The fundamental formula

Mass per metre is:

mass per metre = cross-sectional area × material density

For ordinary carbon steel, a commonly used theoretical density is approximately:

7,850 kg/m³

That gives two convenient formulas:

If area A is in cm²

kg/m = A × 0.785

If area A is in mm²

kg/m = A × 0.00785

These are theoretical calculations. Use the density required for the actual alloy if it differs materially from carbon steel.

Example: HEB 200

A current ArcelorMittal table gives HEB 200 / HE 200 B:

• area ≈ 78.1 cm²;
• published mass ≈ 61.3 kg/m.

Using the formula:

78.1 × 0.785 ≈ 61.3 kg/m

This is a useful check and also shows why an earlier hand calculation based only on web and flange rectangles can give the wrong answer.

Why the simple H-beam rectangle formula is only approximate

A quick idealized I-section area is:

A ≈ 2 × b × tf + (h − 2tf) × tw

where:

• h = overall depth;
• b = flange width;
• tw = web thickness;
• tf = flange thickness.

Then:

kg/m ≈ A × 0.00785

if A is in mm².

For a rolled section, this approximation omits the root fillets and other exact profile geometry. The difference can be significant enough that the published mass should be used for quotations and tonnage calculations.

See How to read beam dimensions.

Fabricated I/H sections

For a welded/fabricated beam made from rectangular plates, the plate-area calculation is often much closer to the real cross-sectional area because there are no rolled root fillets.

However, exact fabrication weight may also include:

• weld metal;
• stiffeners;
• end plates;
• connection plates;
• local reinforcements.

So distinguish section unit weight from the total fabricated-member weight.

What about RHS and SHS?

A simple sharp-corner approximation for a rectangular hollow section is:

A ≈ B × H − (B − 2t)(H − 2t)

where B and H are outside dimensions and t is wall thickness.

But real RHS/SHS have corner radii. For standard products, published manufacturer/standard mass is preferable when accuracy matters.

See HSS, RHS, SHS and CHS terminology.

Use published nominal mass for standard profiles

The current EN 10365:2026 specifies nominal dimensions and masses for many standard hot-rolled European/British section families.

Manufacturer databases such as the ArcelorMittal Orange Book and British Steel section tables provide working values for:

• kg/m;
• area;
• h/b/tw/tf;
• second moments of area;
• section moduli and other properties.

For American W-shapes, AISC provides an official shapes database in both U.S. customary and metric units.

Do not derive unit weight from the section name

Examples:

• HEB 200 is not “200 × 200 × some assumed thickness”;
• IPE 260 does not encode kg/m in its name;
• HEA 550 does not mean 550 kg/m;
• W16×89 does include nominal weight per foot in the American designation, but that naming convention is specific to W-shapes.

The designation system itself must be understood before using it in calculations.

Nominal mass vs actual delivered weight

Published kg/m is a nominal/theoretical mass based on nominal geometry and density.

Actual delivered mass can vary because of:

• dimensional tolerances;
• rolling tolerances;
• actual chemistry/density;
• cutting length tolerance;
• coatings or surface condition where relevant.

Commercial contracts may be based on theoretical weight or actual weighed tonnage. Check the quotation and PO basis.

A practical procurement workflow

For a standard profile:

1. identify the exact section designation;
2. confirm the dimensional standard;
3. take kg/m from the current standard/mill table;
4. multiply by ordered length and quantity;
5. confirm whether commercial invoicing is theoretical or actual weight.

For a custom fabricated profile:

1. calculate the component areas;
2. multiply by density;
3. add other components/weld allowances if needed;
4. verify against fabrication drawings.

MetalMate takeaway

Use published mass-per-metre data for standard rolled sections. Use area × density for custom sections. A simple web-and-flange formula is useful as a check, but it should not replace the official section table for HE/IPE/UB/UC profiles.

Related Knowledge

• HEA, HEB, HEM and IPE sections
• How to read beam dimensions
• UB, UC and American W-sections vs European HE/IPE
• HSS, RHS, SHS and CHS terminology
• Rolled beam vs welded/fabricated beam

References

• NEN, EN 10365:2026 — Hot rolled steel channels, I and H sections — Dimensions and masses: https://www.nen.nl/en/nen-en-10365-2026-en-353950
• ArcelorMittal Orange Book, HE section dimensions and properties: https://orangebook.arcelormittal.com/node/16
• ArcelorMittal Orange Book, IPE section dimensions and properties: https://orangebook.arcelormittal.com/node/6
• AISC, Shapes Database v16.0: https://www.aisc.org/aisc/publications/steel-construction-manual/aisc-shapes-database-v160/