At the same weight, a C-channel is usually deeper and stronger in bending about its strong axis, but a square tube is far stronger at everything else: bending sideways, resisting twist and carrying load as a post. In our comparison below, at the same 12.2 kg/m, a square HSS is about 95 times stiffer in torsion than a C150 channel and, as a 2.4 m post, carries roughly three to four times the load. Which one is "stronger" depends on what the member has to do.
The shapes being compared
- C-channel: a hot-rolled channel such as C150x12, about 152 mm deep with one flat back and two flanges. See the C-channel size chart.
- Square and rectangular tube: hollow structural sections (HSS), such as HSS 89x89x4.8 or HSS 102x76x4.8, closed on all four sides. See the HSS size chart.
The key difference is open versus closed. A channel is an open section: its walls don't form a loop. A tube is closed. That single fact explains most of the comparison.
Equal weight, side by side
These three sections all weigh 12.2 kg/m, so the steel cost per metre is about the same. HSS properties are from the CISC structural section tables; channel properties are from the AISC Shapes Database metric columns.
| Property | C150x12 | HSS 89x89x4.8 | HSS 102x76x4.8 |
|---|---|---|---|
| Depth x width (mm) | 152 x 49 | 89 x 89 | 102 x 76 |
| Strong-axis I, Ix (10⁶ mm⁴) | 5.45 | 1.79 | 2.18 |
| Strong-axis S, Sx (10³ mm³) | 71.3 | 40.3 | 43.0 |
| Weak-axis I, Iy (10⁶ mm⁴) | 0.286 | 1.79 | 1.39 |
| Weak-axis r, ry (mm) | 13.6 | 34.0 | 30.0 |
| Torsional constant J (10³ mm⁴) | 30.6 | 2,920 | 2,780 |
Bending on the strong axis: the channel wins clearly. Because it's deeper, it has about three times the Ix of the square tube and about 1.8 times the section modulus. For a well-braced beam loaded straight down through its shear centre, the channel is the stiffer, stronger member at this weight.
Bending on the weak axis: the tube wins by a mile. The square tube's weak-axis inertia is more than six times the channel's.
Twisting: this is where a closed section shines. The tube's torsional constant is about 95 times the channel's. An open channel twists easily, and its shear centre sits behind the web, so ordinary loads make it twist. A tube barely notices.
As a post or column
Posts buckle about their weakest axis, so the weak-axis radius of gyration matters most. As an illustration, using the CSA S16 column formula for an axially loaded member with both ends pinned, a 2.4 m length and 350 MPa steel for both:
| Section (12.2 kg/m) | Slenderness KL/r | Factored compressive resistance (illustration) |
|---|---|---|
| C150x12 | 176 | about 82 kN |
| HSS 89x89x4.8 | 71 | about 309 kN |
| HSS 102x76x4.8 | 80 | about 273 kN |
Same steel, same weight, and the square tube carries nearly four times as much. And the channel's figure is optimistic: open sections can also buckle by twisting, which reduces it further. For posts, columns and anything in compression, tube beats channel. These are comparison figures, not design values; a real post is designed for its actual loads, end conditions and connections.
Same outside size, different story
People often compare a C100 channel with a 102 mm square tube because they look similar on a drawing. They're not similar members:
| Section | Mass (kg/m) | Ix (10⁶ mm⁴) | Iy (10⁶ mm⁴) | J (10³ mm⁴) |
|---|---|---|---|---|
| C100x8 | 8.0 | 1.60 | 0.130 | 16.6 |
| HSS 102x102x3.2 | 9.7 | 1.96 | 1.96 | 3,080 |
| HSS 102x102x4.8 | 14.1 | 2.75 | 2.75 | 4,440 |
At the same outside depth, even the thin-wall tube beats the channel on every property, for only a little more weight.
Is C-channel cheaper than square tubing?
We don't publish prices, but we can tell you what drives the difference:
- Weight. Steel is largely bought by weight, so compare sections at the mass each design actually needs, not by outside size.
- Fabrication. A channel's flat back is easy to bolt or weld to, and the open shape is easy to paint and inspect. Tubes often need end caps or plates, and galvanized tubes need vent and drain holes.
- Connections. Bolting through a tube wall needs care (through-bolts, sleeves or welded tabs). Welding to a tube is straightforward.
- Availability. Common sizes of both are stocked; less common weights take longer. Ask what's on the rack before you design around it.
If your designer will accept either, ask for pricing on both options for your actual quantities.
Practical details that change the choice
Strength tables don't capture everything that happens in the shop and on site:
- Corrosion. An open channel drains and dries and every surface can be painted and inspected. A tube's inside can't be painted after it's closed, so exterior tubes are either sealed with caps or galvanized inside and out. Moisture trapped inside an unsealed tube can rust it from the inside.
- Attachments. Clips, tabs and plates weld easily to either shape. Bolting through the flange of a channel needs bevelled washers because of the sloped inner face; bolting through a tube wall needs sleeves or through-bolts so the wall isn't crushed.
- Appearance. Tubes give clean, flat faces on all four sides, which is why they're popular for exposed posts and railings.
- Fit-up. A channel's open side can wrap around or nest against other members, which is handy for framing and ledgers.
Which to use
| Use | Usually better | Why |
|---|---|---|
| Post, column, bollard | Square tube | Buckling resistance in every direction |
| Gate or frame that sees twisting | Tube | Torsional stiffness |
| Trailer or equipment frame rail | Either, by design | Channels bolt easily; tubes resist twist |
| Stair stringer | Channel | Flat back, open side for treads |
| Ledger or edge member against a wall | Channel | Flat back for anchors |
| Braced beam on its strong axis | Channel (or a W-shape) | Depth gives bending stiffness |
| Railing posts and rails | Tube | Clean look, stiff in all directions |
Two channels welded toes together, or closed with plates, form a box section that behaves much more like a tube. It's a useful option when you need a size or shape that isn't stocked, but the welds have to be designed for the job.
For beams carrying floors, neither may be the best answer; a W-shape is usually more efficient. See C-channel vs I-beam and W-beam vs HSS.
Channels and tubes, cut and fabricated
We supply C-channels and HSS posts cut to length and fabricated to your drawings, with base and cap plates, holes and connection plates, and CWB-certified shop welding. If your drawings leave the choice open, we can quote both.
Send your drawings for a quote, or browse our steel products for posts, channels, beams and plates.
Frequently asked questions
Is C-channel stronger than square tubing?
At the same weight, a C-channel is usually deeper and stronger in bending about its strong axis. A square tube is far stronger in every other way: sideways bending, twisting and as a column or post. Which is stronger depends on how the member is loaded and braced.
Is C-channel stronger than rectangular tubing?
For a beam loaded on its deep axis and well braced, a channel of the same weight is often stiffer because it is deeper. A rectangular tube of the same weight resists twisting and buckling much better, so it usually wins for unbraced beams, posts and frames.
Is C-channel cheaper than square tubing?
It depends on the size, the steel weight, the fabrication and what is in stock. Open channels are easy to bolt to, coat and inspect, while tubes may need end caps or vent holes. Ask for a quote on both if your designer allows either.
Can I box two channels to make a tube?
Yes. Two channels welded toes together, or closed with plates, make a box section that resists twisting far better than a single channel. Whether it beats a stock tube depends on the size, and the welding has to be designed.
