Channel (C-shape) properties
Section properties for standard AISC C-channels: depth, weight, area, moment of inertia, and section modulus about the strong axis. Channels are used for frames, supports, and members where a flat back is handy.
American Standard Channels (C), strong axis
| Section | Depth (in) | Weight (lb/ft) | Area (in²) | Ix (in⁴) | Sx (in³) |
|---|---|---|---|---|---|
| C3x4.1 | 3 | 4.1 | 1.20 | 1.65 | 1.10 |
| C4x5.4 | 4 | 5.4 | 1.58 | 3.85 | 1.92 |
| C5x6.7 | 5 | 6.7 | 1.97 | 7.48 | 3.00 |
| C6x8.2 | 6 | 8.2 | 2.39 | 13.1 | 4.35 |
| C6x10.5 | 6 | 10.5 | 3.08 | 15.1 | 5.04 |
| C7x9.8 | 7 | 9.8 | 2.87 | 21.2 | 6.07 |
| C8x11.5 | 8 | 11.5 | 3.37 | 32.5 | 8.14 |
| C9x13.4 | 9 | 13.4 | 3.94 | 47.8 | 10.6 |
| C10x15.3 | 10 | 15.3 | 4.48 | 67.3 | 13.5 |
| C12x20.7 | 12 | 20.7 | 6.08 | 129 | 21.5 |
Channels are named by depth and weight per foot, so a C8x11.5 is 8 inches deep at 11.5 lb/ft. Ix and Sx are for bending about the strong (X) axis, with the web vertical. The section is much weaker about the Y axis and tends to twist under load, since its shear center sits outside the web, so channels are often used in pairs or with the load near the back.
Comparing against beams?
See the Steel Beam Properties Chart for wide-flange W shapes.
When to use a channel
Channels suit framing, rails, supports, and built-up members where the flat back is useful for bolting against a surface. A single channel bends efficiently about its strong axis, but its open C section makes it prone to twisting, so for pure bending a wide-flange beam is more efficient. Two channels joined back to back form a strong, symmetric box.
Reading Ix and Sx
Ix, the moment of inertia, governs deflection: a higher value means a stiffer member. Sx, the section modulus, governs bending strength: a higher value means lower bending stress for a given moment. Both increase sharply with depth, so a deeper channel of the same weight carries far more.
FAQ
What does C8x11.5 mean?
A standard channel 8 inches deep weighing 11.5 pounds per foot. The first number is depth, the second is weight per foot.
Why do channels twist under load?
Their shear center lies outside the web, so a load through the section also applies a twisting moment unless it passes through that point. Pairing channels or restraining them avoids the twist.
Are channels as strong as I-beams?
For the same weight a wide-flange beam is stiffer and stronger in bending and does not twist, so beams are preferred for pure bending. Channels win where the flat back or lighter sections are useful.