I-Beam Sizes (S-Shape)

Nominal dimensions and weights for 25 American Standard S-shape beams, in inches and millimetres.

Page last changed 2026-10-19 · based on ASTM A6/A6M-24

American Standard S-Shape Beams (ASTM A6)

S-shapes are the older American Standard beam, with tapered flanges. The taper makes them easier to roll but harder to bolt to — a connection plate bears only on the thin edge of the flange — which is the main reason W-shapes displaced them. They survive in existing structures and in some crane rails and monorails where the tapered flange suits the wheel profile.

Their depth is exactly nominal, which is a real difference from wide-flange shapes: an S8 is 8.00 in deep and an S10 is 10.00, while W8 and W10 sections vary around their nominal depth depending on weight. Where an existing structure must be measured to identify its members, that exactness is a useful clue.

The weight column is exact because the designation states it, and the area column is derived from the weight — so it includes the fillets the nominal dimensions omit. Section properties are deliberately not given: take them from the AISC Shapes Database.

Tapered Flange Against Parallel Flange

The difference between an S-shape and a W-shape is entirely in the flange, and it changes how the beam is used rather than how it carries load.

A tapered flange is thinner at the toe than at the root. That makes the section efficient in bending — material sits where the stress is highest — and it makes the shape easier to roll. But a bolted connection bears on the flange face, and a tapered face gives a line contact at the toe rather than full bearing, so connection plates must be bevelled or the bolts are loaded eccentrically.

A parallel flange gives full bearing across its width, which is why every modern bolted connection assumes a W-shape. Welded connections do not care — a weld follows the surface either way — which is why S-shapes remain serviceable in welded construction.

Where a drawing specifies an S-shape today, the question worth asking is whether the designer needed the taper for a wheel to run on, or simply copied an existing detail. Substituting a W-shape of equivalent capacity is usually possible and usually cheaper.

Frequently Asked Questions

What is an S-shape beam?

An American Standard beam — the older rolled I-section with tapered flanges. The designation gives nominal depth and weight per foot, so S8×18.4 is 8 in deep and weighs 18.4 lb/ft. Parallel-flange W-shapes have largely replaced them.

What is the difference between an S-beam and a W-beam?

The flange. S-shapes have tapered flanges and exactly nominal depth; W-shapes have essentially parallel flanges and a depth that varies around nominal. Parallel flanges give full bearing for bolted connections, which is why W-shapes displaced S-shapes.

How much does an S8x18.4 weigh?

18.4 lb/ft, or 27.4 kg/m. The weight is stated in the designation, so a 20 ft length weighs 368 lb. Delivered weight is within a few percent because of rolling tolerance, usually slightly under nominal.

Where are S-shapes still used?

In existing structures where they were originally specified, and in some crane rails and monorails where the tapered flange matches the wheel profile. For new work a W-shape of equivalent capacity is normally specified instead.

Where do I find S-shape section properties?

In the AISC Shapes Database or an equivalent table. The nominal dimensions on this page do not describe the fillets, so a moment of inertia computed from them comes out low by 2 to 3%.

Related

• W-Shape Steel Beam Sizes
• Metric H-Beam Sizes
• C-Channel Sizes
• Section Properties
• ASTM A992 Beam Steel

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

Data Sources

Verification scope

No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.

Derived values — the following values on this page are calculated, not taken directly from the standard:

Weights are exact as stated in the designation and dimensions are nominal. Section properties are not given — take them from the AISC Shapes Database. S-shapes are the older tapered-flange series; confirm whether a design actually requires one before substituting a W-shape of equivalent capacity.

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