C-channel is an open structural section with a web and two flanges forming a C-profile. It resists bending efficiently when loaded so the flanges carry tension and compression, and its flat back face makes it straightforward to mount, weld, and bolt. The full designation system, dimension data, and fabrication details for all three channel families are below.
Three Types of Channel
Standard C-channel (C-shape): Features a tapered inner flange — thicker at the web junction, thinner at the tip, at approximately 16° taper from horizontal. Designation: C[depth] × [weight per foot].
MC-channel (Miscellaneous channel): Parallel flanges — both inner and outer flange faces are flat and parallel. Required when a flat bearing surface inside the flange is needed. Designation: MC[depth] × [weight per foot].
Bar channel: Smaller sections sold by leg length and thickness rather than depth and weight. Used for light framing, door frames, and enclosures.
Within a given depth group, heavier weight = thicker web + wider flange.
Standard C-Channel Dimensions
All data from AISC Steel Construction Manual, ASTM A36.
| Designation | Depth (in) | Flange Width (in) | Flange Thickness (in) | Web Thickness (in) | Weight (lb/ft) |
|---|---|---|---|---|---|
| C3 × 4.1 | 3.00 | 1.410 | 0.273 | 0.170 | 4.1 |
| C3 × 5.0 | 3.00 | 1.498 | 0.273 | 0.258 | 5.0 |
| C4 × 5.4 | 4.00 | 1.584 | 0.296 | 0.184 | 5.4 |
| C4 × 7.25 | 4.00 | 1.721 | 0.296 | 0.321 | 7.25 |
| C5 × 6.7 | 5.00 | 1.750 | 0.320 | 0.190 | 6.7 |
| C5 × 9.0 | 5.00 | 1.885 | 0.320 | 0.325 | 9.0 |
| C6 × 8.2 | 6.00 | 1.920 | 0.343 | 0.200 | 8.2 |
| C6 × 10.5 | 6.00 | 2.034 | 0.343 | 0.314 | 10.5 |
| C6 × 13.0 | 6.00 | 2.157 | 0.343 | 0.437 | 13.0 |
| C7 × 9.8 | 7.00 | 2.085 | 0.366 | 0.210 | 9.8 |
| C7 × 12.25 | 7.00 | 2.194 | 0.366 | 0.314 | 12.25 |
| C8 × 11.5 | 8.00 | 2.260 | 0.390 | 0.220 | 11.5 |
| C8 × 13.75 | 8.00 | 2.343 | 0.390 | 0.303 | 13.75 |
| C8 × 18.75 | 8.00 | 2.527 | 0.390 | 0.487 | 18.75 |
| C9 × 13.4 | 9.00 | 2.433 | 0.413 | 0.233 | 13.4 |
| C9 × 20.0 | 9.00 | 2.648 | 0.413 | 0.448 | 20.0 |
| C10 × 15.3 | 10.00 | 2.600 | 0.436 | 0.240 | 15.3 |
| C10 × 20.0 | 10.00 | 2.739 | 0.436 | 0.379 | 20.0 |
| C10 × 25.0 | 10.00 | 2.886 | 0.436 | 0.526 | 25.0 |
| C12 × 20.7 | 12.00 | 2.942 | 0.501 | 0.282 | 20.7 |
| C12 × 25.0 | 12.00 | 3.047 | 0.501 | 0.387 | 25.0 |
| C12 × 30.0 | 12.00 | 3.170 | 0.501 | 0.510 | 30.0 |
| C15 × 33.9 | 15.00 | 3.400 | 0.650 | 0.400 | 33.9 |
| C15 × 40.0 | 15.00 | 3.520 | 0.650 | 0.520 | 40.0 |
| C15 × 50.0 | 15.00 | 3.716 | 0.650 | 0.716 | 50.0 |
MC-Channel Dimensions
MC-channel has parallel flanges and different section proportions from standard C. Verify availability with your local service center before designing around a specific MC designation.
| Designation | Depth (in) | Flange Width (in) | Flange Thickness (in) | Web Thickness (in) | Weight (lb/ft) |
|---|---|---|---|---|---|
| MC3 × 7.1 | 3.00 | 1.938 | 0.350 | 0.312 | 7.1 |
| MC6 × 12.0 | 6.00 | 2.497 | 0.375 | 0.310 | 12.0 |
| MC6 × 15.3 | 6.00 | 2.667 | 0.375 | 0.340 | 15.3 |
| MC8 × 18.7 | 8.00 | 2.978 | 0.425 | 0.353 | 18.7 |
| MC8 × 22.8 | 8.00 | 3.502 | 0.525 | 0.427 | 22.8 |
| MC10 × 28.5 | 10.00 | 3.950 | 0.575 | 0.425 | 28.5 |
| MC12 × 35.0 | 12.00 | 3.767 | 0.700 | 0.600 | 35.0 |
The 16° Flange Taper: What It Means in Practice
Standard C-channel flanges taper at approximately 16° from horizontal — thicker at the web, thinner at the tip.
Three practical consequences:
-
Gusset plates: A flat gusset designed to sit flush inside the flange will bear at the web edge and gap at the tip. Design gussets to contact the flange root only, or specify MC-channel when full-face contact is required.
-
Fillet welds to inside face: The taper limits effective gun or electrode angle. For critical connections to the inside flange face, use MC-channel with parallel flanges.
-
Back-to-back channel: Two C-channels placed back-to-back produce a box section where the flange tips angle outward — acceptable for structural use but means flange-to-flange welding is slightly awkward.
C vs MC decision:
| Requirement | Use C | Use MC |
|---|---|---|
| General structural bending | Yes | Yes |
| Conveyor track (items ride on flange) | No | Yes |
| Flat mount plate sits in channel | No | Yes |
| Back-to-back, parallel faces | Acceptable | Preferred |
| Maximum availability | Yes | Limited |
Back-to-Back Channel: Building a Box Section
Two C-channels placed web-to-web and welded form a closed rectangular box section with significantly better torsional rigidity than an open channel.
Standard gap: 3/8" to 1/2" between webs to allow fillet welds on both web faces along the length.
Weld pattern: Intermittent fillet welds at 12" spacing for non-pressure applications. Continuous weld for members subject to shear flow or fatigue.
Box section capacity: Two C8 × 11.5 channels back-to-back carry approximately double the moment of inertia of a single channel about the strong axis, plus torsional stiffness the open channel entirely lacks.
Approximate Safe Spans
Simply supported beam, 200 lb/ft uniform load, A36 steel, L/360 deflection limit:
| Designation | Ix (in⁴) | Approx. Span Limit |
|---|---|---|
| C5 × 6.7 | 7.49 | ~6 ft |
| C6 × 8.2 | 13.1 | ~7 ft |
| C8 × 11.5 | 32.6 | ~10 ft |
| C10 × 20.0 | 78.9 | ~14 ft |
| C12 × 25.0 | 144 | ~17 ft |
| C15 × 33.9 | 315 | ~22 ft |
Preliminary sizing only. Structural design requires full load calculation per applicable codes.