Angle Iron Sizes

Equal Leg Steel Angles

The area formula is exact for a sharp-cornered angle; real angles have a rounded heel and toe that make them very slightly smaller. In practice the difference is under 1%, which is why the computed weights reproduce published values closely — but it is a derived figure, not a tabulated one, and a weight-critical calculation should use the mill's figure.

An angle is not symmetric about either axis, and like a channel its shear centre is not at the centroid. It has principal axes rotated relative to the legs, so it bends about an axis at roughly 45° to the legs rather than about either one. That makes hand calculation unreliable and is why angles are usually selected from tables with the principal-axis properties already worked out.

Angles are commonly used in pairs — back to back, or as the two legs of a built-up T — which restores symmetry and makes the section far easier to design with. Where an angle must work alone, its bracing and its connection both have to account for the eccentricity.

Equal and Unequal Leg Angles

Both types exist, and the difference matters more than it appears.

Equal leg angles are the general-purpose series, stocked in the widest range of sizes and used for bracing, frames, brackets, lintels and edge stiffeners. They are symmetric about one diagonal — the line through the heel at 45° — which simplifies the section properties somewhat.

Unequal leg angles are made for connections where one leg bolts to a member and the other does the work, and for situations where the load needs more depth in one direction. They are less widely stocked, and the asymmetry is more pronounced.

Both are specified the same way: legs then thickness. An unequal angle adds a third dimension — L4×3×1/4 is a 4 in leg and a 3 in leg with a 1/4 in thickness.

For new work, angle selection should account for the fact that legs are normally thinner than the section they connect to, so bearing and edge distance at the bolts are often what limits the connection rather than the angle's own capacity.

Frequently Asked Questions

How is an angle size written?

Leg × leg × thickness for an equal leg angle — L3×3×1/4 is 3 in on both legs and 1/4 in thick. An unequal angle adds a third dimension, so L4×3×1/4 has a 4 in leg and a 3 in leg.

How do I calculate the weight of an angle?

Area = (2 × leg − thickness) × thickness, then weight per foot = area × 12 × 0.2836. For L3×3×1/4 that is (6 − 0.25) × 0.25 = 1.4375 in² and 4.90 lb/ft, which matches the published figure.

Why does an angle behave differently from a channel or I-beam?

Because it is not symmetric about either leg, so its principal axes are rotated about 45° to the legs. It bends about that diagonal rather than about a leg, which makes hand calculation unreliable — use published tables with the principal-axis properties.

What are angles used for?

Bracing, frames, brackets, lintels, edge stiffeners and connections. They are cheap and widely stocked, which makes them the default for anything light-duty that needs stiffness in two directions without the depth of a channel.

Do angles come in unequal legs?

Yes — written with both legs, such as L4×3×1/4. They are used where one leg bolts to a member and the other does the work, or where more depth is needed in one direction. They are less widely stocked than equal leg angles.

Related

• C-Channel Sizes
• I-Beam Sizes (S-Shape)
• Section Properties
• Steel Plate Sizes
• ASTM A36 Steel Properties

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:

Areas and weights are derived from the nominal geometry, which omits the rounded heel and toe — the error is under 1%. Section properties are not given: an angle's principal axes are rotated relative to its legs, so those values should come from a table rather than being calculated from the legs.

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