How to read beam dimensions: h, b, tw, tf and root radius

A rolled I- or H-section is usually described by a small set of geometric dimensions. The symbols are simple once you know them, but different catalogues do not always use exactly the same letters.

The most common European-style notation is:

These dimensions define the basic geometry of profiles such as IPE, HEA, HEB and HEM.

The same dimensions may use different letters

Do not assume every catalogue uses h, b, tw and tf.

For example, British section tables commonly use:

• D for depth;
• B for width;
• t for web thickness;
• T for flange thickness;
• r for root radius.

The geometry is the same concept; the notation changes.

Therefore when reading an unfamiliar table, check its heading or diagram before copying values.

Example: HE 200 B / HEB 200

A current ArcelorMittal section table gives approximately:

This is why the shorthand “HEB 200” is not enough if you specifically need the web or flange thickness.

For comparison with HEA, HEM and IPE, see HEA, HEB, HEM and IPE: practical differences.

What is the root radius?

The root radius is the internal fillet where the web blends into the flange on a rolled section.

It matters for:

• clear flat web depth;
• cope and notch detailing;
• connection plates;
• bolt clearance;
• local geometry;
• accurate cross-sectional area and mass.

It should not be confused with the outside corner radius of a rectangular hollow section.

What is “depth between fillets”?

Section tables often contain another dimension such as d, meaning the clear depth of web between the root fillets.

This is useful when checking whether a plate, connection, stiffener or bolt arrangement can physically fit between the flange fillets.

Again, notation varies by source, so use the table definition rather than assuming the symbol.

Nominal section size is not always actual h

This causes many purchasing errors.

Examples from the same nominal HE family can have different actual heights. In the 200 family:

• HE 200 A is around 190 mm deep;
• HE 200 B is around 200 mm;
• HE 200 M is around 220 mm.

So “HE 200” without the suffix is incomplete.

The same principle applies when comparing European profiles with UB, UC or W-sections.

What dimensions matter when proposing a substitute?

Do not compare only h and b.

At minimum compare:

• h / overall depth;
• b / flange width;
• tw / web thickness;
• tf / flange thickness;
• root radius;
• mass per metre;
• cross-sectional area;
• second moments of area;
• elastic/plastic section modulus;
• connection geometry.

A replacement can be heavier yet still fail a specific dimensional or structural requirement.

Rolled versus fabricated sections

For a fabricated or welded beam, h, b, tw and tf can often be chosen directly from plate dimensions.

For a rolled beam, they are fixed by the standardized/mill section geometry, including root fillets.

This distinction also affects how accurately a simple rectangular-area formula can predict the section’s unit weight.

MetalMate takeaway

For I/H sections, learn five dimensions first: h, b, tw, tf and r. But always check the catalogue notation, because British, European and American tables may use different symbols for the same geometry.

Related Knowledge

• HEA, HEB, HEM and IPE sections
• UB, UC and American W-sections vs European HE/IPE
• Rolled beam vs welded/fabricated beam
• Steel-section unit weight

References

• ArcelorMittal Orange Book, HE section properties and dimension notation: https://orangebook.arcelormittal.com/node/16
• British Steel, UK sections dimensions and properties: https://britishsteel.co.uk/media/jlybepgw/uk-sections-datasheets-100723.pdf
• NEN, EN 10365:2026 — Dimensions and masses of hot rolled channels, I and H sections: https://www.nen.nl/en/nen-en-10365-2026-en-353950