How much weight a C-channel can hold depends on its size, span, orientation, bracing and grade, so there's no single rating. Stood upright with its top flange braced, a C150x12 (C6x8.2) in 350W steel has a factored bending resistance of about 27 kN·m; over a 3 m span that's roughly 24 kN/m of factored load in bending, but only about 8.6 kN/m before it sags past span/360. Laid flat, the same channel is about 19 times less stiff. And because a channel's shear centre sits behind its web, an unbraced channel twists and carries less again. Here's how channel capacity is worked out, with real Canadian section values.
These numbers illustrate the method. A channel carrying a floor, roof, stair or equipment needs to be designed by an engineer, and most structural work in Ontario needs a permit.
What controls a channel's capacity
Five things decide what a hot-rolled C-channel can carry:
- Size. Depth matters most. Going from C150 to C200 roughly doubles bending resistance.
- Span. For a uniform load, bending capacity falls with the square of the span and stiffness with the cube.
- Orientation. Web vertical ("upright") is the strong way. Web horizontal ("flat", like a tray) is dramatically weaker.
- Bracing and twisting. A channel loaded through its web wants to roll. Bracing, or a load applied in line with the shear centre, controls that.
- Grade. Canadian channels are commonly 350W or 300W, or ASTM A36 or A572 Grade 50. The resistance scales with yield strength: an A36 channel (250 MPa) has about 71% of the bending resistance of the same channel in 350W. See steel channel grades.
C-channel load capacity chart: bending resistance
The table lists the factored moment resistance for common channels in two orientations. Section properties are from the AISC Shapes Database metric columns for the equivalent imperial channels. Upright values use Mr = 0.90 x Zx x 350 MPa and assume the channel is fully braced and loaded through its shear centre. Flat values use the elastic section modulus (a conservative simplification) and are shown to make the contrast clear.
| Channel | Imperial | Mass (kg/m) | Mr upright (kN·m) | Mr flat (kN·m) | Stiffness ratio, upright to flat |
|---|---|---|---|---|---|
| C100x8 | C4x5.4 | 8.0 | 11.8 | 1.4 | 12 |
| C150x12 | C6x8.2 | 12.2 | 26.6 | 2.5 | 19 |
| C200x17 | C8x11.5 | 17.1 | 49.8 | 4.0 | 25 |
| C250x23 | C10x15.3 | 22.8 | 82.2 | 5.9 | 30 |
| C310x31 | C12x20.7 | 30.8 | 132 | 8.9 | 33 |
| C380x50 | C15x33.9 | 50.4 | 262 | 15.9 | 39 |
To convert a moment resistance into a load on a simple span: maximum factored uniform load = 8 x Mr / L², and maximum factored mid-span point load = 4 x Mr / L. Then check deflection, which often governs.
For dimensions and every standard size, see our C-channel size chart.
Upright vs flat: the same channel, two answers
Here is a C150x12 over three short spans, simply supported with a uniform load. "Bending" is the maximum factored load. "Deflection" is the specified (unfactored) load that makes it sag span/360.
| Span | Upright: bending | Upright: deflection | Flat: bending | Flat: deflection |
|---|---|---|---|---|
| 2.0 m | 53 kN/m | 29 kN/m | 5.0 kN/m | 1.5 kN/m |
| 2.4 m | 37 kN/m | 17 kN/m | 3.5 kN/m | 0.88 kN/m |
| 3.0 m | 24 kN/m | 8.6 kN/m | 2.2 kN/m | 0.45 kN/m |
(1 kN is roughly the weight of 102 kg.)
The flat channel over 3 m reaches span/360 under less than half a kilonewton per metre, about 46 kg per metre of span. That's why a channel laid flat across an opening, a trailer frame or a shelf feels springy, and why it's rarely the right way to carry a real load. If a member must be shallow, look at a C-channel vs square tube comparison or a flat plate in a different detail.
Why braced numbers overstate an unbraced channel
The upright numbers above assume the channel can't twist or move sideways. In practice, a channel has two weaknesses an I-beam doesn't:
- Its shear centre is outside the section. For a C150x12, the AISC database puts it about 15 mm behind the back of the web. A load applied through the web or the flanges is offset from that point, so it bends and twists the channel.
- Its weak-axis stiffness is low. The upright-to-flat ratios in the chart show it. Low weak-axis stiffness means an unbraced channel buckles sideways at a lower moment than its braced resistance.
Engineers handle this by bracing the channel at close spacing, fastening it continuously to a wall, slab or deck, connecting loads on the back of the web, or pairing two channels into a symmetric section. When none of that is possible, a W-shape or HSS is usually the better choice. We compare the shapes in C-channel vs I-beam, and look at span and torsion limits in can C-channel be used as a beam.
Steel channel design example
Given: a C150x12 trimmer spanning 2.4 m between two beams, framing a floor opening. Floor joists spanning 3.6 m hang from one side of it in joist hangers, so it carries half the joist span: a 1.8 m tributary width. The joists are at 400 mm centres and brace the channel's top flange. We'll use 1.5 kPa dead and 1.9 kPa live, the loads behind the Ontario code's house beam tables.
Loads:
- Dead: 1.5 x 1.8 = 2.7 kN/m, plus 0.12 kN/m self-weight = 2.82 kN/m
- Live: 1.9 x 1.8 = 3.42 kN/m
- Factored: 1.25 x 2.82 + 1.5 x 3.42 = 8.66 kN/m (2024 OBC Table 4.1.3.2.-A, case 2)
Bending: Mf = 8.66 x 2.4² / 8 = 6.2 kN·m, against Mr = 26.6 kN·m. About 23% used.
Deflection under live load: 5 x 3.42 x 2,400⁴ / (384 x 200,000 x 5.45 x 10⁶) = 1.4 mm, against a span/360 limit of 6.7 mm.
So bending and deflection are easy. What actually governs this member is the twisting. All the joists hang off one face, so every load is offset from the shear centre. The engineer has to check the torsion, the hanger and end connections, and the bracing the joists provide, and might choose a heavier channel, a pair of channels or a W-shape as a result. On short channels, connections and twisting decide the design far more often than plain bending does.
About C-channel load and deflection calculators
Online C-channel load calculators and deflection calculators usually ask for a section, span and load, and return stress and deflection. Before trusting one:
- Check the product. Many tables online are for cold-formed C-sections (light-gauge studs, joists and purlins), which are a different product designed under a different standard. Hot-rolled C-channels are what fabricators supply for structural framing.
- Check the shape library. UK and Australian tools use parallel flange channels (PFC), not North American C-shapes.
- Check the assumptions. Most assume full bracing and a load through the shear centre, which is the best case.
- Check the code basis. US tools use different load and resistance factors from the Ontario code and CSA S16.
A calculator is useful for understanding why a size works. The design for construction comes from your engineer.
Getting channels cut and fabricated
We supply C-channel cut to length and fabricated with holes, copes, clips and welded plates, to your shop drawings or the engineer's details, along with the beams and posts it connects to. If a channel on your drawings is hard to source, ask your engineer for an approved alternate before ordering.
Send your drawings for a quote, or browse our steel products, including C-channels, beams and plates.
Frequently asked questions
How much weight can a C-channel support?
It depends on the channel size, the span, which way it is turned, how it is braced and the steel grade. Standing upright and braced, a C150x12 has a factored bending resistance of about 27 kN·m in 350W steel; laid flat, its bending resistance and stiffness are a small fraction of that.
Is C-channel stronger upright or flat?
Upright, by a wide margin. With the web vertical, a C150x12 is about 19 times stiffer than the same channel laid flat on its back, and a C200x17 about 25 times stiffer.
Why does a C-channel twist under load?
A channel's shear centre sits outside the section, behind the web. A load applied through the web or flanges is offset from that point, so it twists the channel as well as bending it, unless the channel is braced or loaded in line with its shear centre.
Is there a load table for steel C-channel in Canada?
The CISC Handbook of Steel Construction publishes section properties and design aids, and the Ontario Building Code's Part 9 beam span tables cover W-shapes only. A channel carrying structural loads is normally designed by an engineer to CSA S16.
