Angle iron — called simply "angle" in AISC notation — is an L-shaped section used for bracing, brackets, shelf supports, frame members, and edge protection. Its geometry provides stiffness in two planes simultaneously, making it one of the most versatile structural shapes in light to medium fabrication.
Equal-Leg vs Unequal-Leg
Equal-leg angles have matching legs: L 4×4×3/8 has two 4" legs and 3/8" thickness. The most common form in general fabrication.
Unequal-leg angles have different leg lengths: L 4×3×3/8 has a 4" leg and a 3" leg, both 3/8" thick. Used when one direction requires more bearing surface or projection than the other — typical in connections where one leg laps a column and the other supports a beam.
Convention: The longer leg is always listed first. L 4×3×3/8 means 4" leg × 3" leg × 3/8" thickness. Reversing the leg order creates ambiguity on shop drawings — always follow the longer-first rule.
Equal-Leg Angle Sizes and Weights
Weights in pounds per linear foot, ASTM A36, from AISC Steel Construction Manual.
| Size | 1/8" | 3/16" | 1/4" | 5/16" | 3/8" | 1/2" | 5/8" | 3/4" | 1" |
|---|---|---|---|---|---|---|---|---|---|
| 1×1 | 0.80 | 1.16 | — | — | — | — | — | — | — |
| 1-1/2×1-1/2 | 1.23 | 1.80 | 2.34 | — | — | — | — | — | — |
| 2×2 | 1.65 | 2.44 | 3.19 | 3.92 | 4.70 | — | — | — | — |
| 2-1/2×2-1/2 | — | 3.07 | 4.10 | 5.00 | 5.90 | 7.70 | — | — | — |
| 3×3 | — | 3.71 | 4.90 | 6.10 | 7.20 | 9.40 | 11.5 | — | — |
| 3-1/2×3-1/2 | — | — | 5.80 | 7.20 | 8.50 | 11.1 | — | — | — |
| 4×4 | — | — | 6.60 | 8.20 | 9.80 | 12.8 | 15.7 | 18.5 | — |
| 5×5 | — | — | — | 10.3 | 12.3 | 16.2 | 20.0 | 23.6 | — |
| 6×6 | — | — | — | 12.3 | 14.9 | 19.6 | 24.2 | 28.7 | 37.4 |
| 8×8 | — | — | — | — | — | 26.4 | 32.7 | 38.9 | 51.0 |
Unequal-Leg Angle Sizes and Weights
| Size | 1/8" | 3/16" | 1/4" | 5/16" | 3/8" | 1/2" |
|---|---|---|---|---|---|---|
| 2×1-1/2 | 1.44 | 2.12 | 2.77 | — | — | — |
| 2-1/2×2 | — | 2.75 | 3.62 | 4.50 | — | — |
| 3×2 | — | 3.07 | 4.10 | 5.00 | 5.90 | — |
| 3×2-1/2 | — | — | 4.50 | 5.60 | 6.60 | — |
| 3-1/2×2-1/2 | — | — | 5.40 | 6.60 | 7.90 | — |
| 4×3 | — | — | 6.20 | 7.70 | 9.10 | 11.9 |
| 5×3 | — | — | 6.60 | 8.20 | 9.80 | 12.8 |
| 5×3-1/2 | — | — | 7.40 | — | 10.4 | 13.6 |
| 6×4 | — | — | — | — | 12.3 | 16.2 |
| 8×6 | — | — | — | — | — | 23.0 |
Choosing Leg Size for Bracket Applications
Fillet weld capacity to an angle leg is limited by the leg width. A longer weld is more effective than a thicker angle for increasing shear capacity.
AWS D1.1 minimum fillet weld sizes:
| Base Metal Thickness | Minimum Fillet Size |
|---|---|
| Up to 1/4" | 1/8" |
| Over 1/4" to 1/2" | 3/16" |
| Over 1/2" to 3/4" | 1/4" |
| Over 3/4" | 5/16" |
For a 3×3×1/4 angle: minimum fillet = 3/16". Maximum fillet to leg edge = 3/16" (leg thickness − 1/16" = 1/4" − 1/16" = 3/16").
Rough bracket load guide:
| Load Level | Typical Angle |
|---|---|
| Light shelf, < 500 lb | L 2×2×3/16 or L 2×2×1/4 |
| Medium bracket, 500–2000 lb | L 3×3×1/4 or L 3×3×3/8 |
| Heavy bracket/machinery, 2000–5000 lb | L 4×4×3/8 or L 4×4×1/2 |
Hot-Rolled vs Laser-Fused Angle
Hot-rolled: Produced by rolling hot steel through grooved rolls. Inner root radius ≈ 1× leg thickness. Mill scale surface. Cost baseline.
Laser-fused: Two flat bar elements joined by laser weld along the inner root. Nearly zero root radius (sharp corner). Excellent straightness. 1.5–2.5× hot-rolled cost. Smaller standard size range.
Specify laser-fused when a tight inner corner is required for a flush fit against a square-edged mating part, or when straightness is critical for a guide rail. For general fabrication, hot-rolled is standard.
When to Buy Angle vs Cut L-Shapes from Plate
Buy angle when:
- The part is long (2 ft+) and uses the angle as a structural member
- Leg widths match a standard angle size exactly
- Consistent thickness across both legs is required
Cut from plate when:
- The L-shape has custom dimensions not in the standard angle range
- Cutouts, holes, or notches are needed (easier to nest on plate)
- The two legs need different thicknesses — impossible in purchased angle
A plasma-cut L-shape has a sharp inside corner; a bent plate L has an inside bend radius. If the inside corner must be sharp for a close fit, cutting from plate is the correct process. If the application allows a radius (most do), bending plate is often faster.