How to Read C-Channel Sizes: Naming, Web and Flange

C-channel names give two numbers: the nominal depth and the weight. In Canadian metric nomenclature, C200x17 means a standard hot-rolled channel about 200 mm deep (actually 203 mm) weighing about 17 kg per metre. The imperial name for the same piece is C8x11.5: 8 inches deep, 11.5 pounds per foot. The flange width and web thickness aren't in the name, so to identify a channel you already have, you measure the depth, the flange width and the web thickness and match them to a section table.

This guide covers the parts of a channel, how to read a channel callout on a drawing, how to measure a channel on site and how to convert between metric and imperial names. For the full size table, see our C-channel sizes chart.

The parts of a C-channel

Standard C-channels have that sloped inside flange face, so the flange is thicker at the web than at the toe. Bolting through a sloped flange needs a bevelled washer to sit flat. MC (miscellaneous) channels have different flange proportions, covered in our post on C channel vs MC channel.

How to read a channel callout

A Canadian structural drawing might show any of these:

• C200x17. Standard channel, 200 mm nominal depth, 17 kg/m.
• C8x11.5. The same section in imperial: 8 inch depth, 11.5 lb/ft. Common on American drawings, older Canadian drawings and some supplier lists.
• MC8x20. A miscellaneous channel, usually named in imperial.
• 2-C250x30 (back to back). Two channels, webs together, often with a gap for a gusset plate, used as a built-up member.
• C310x31 (toes in). Orientation note for a channel used as a lintel, edge member or stair stringer.

The first number is a family name, not an exact measurement. Every C200 is 203 mm deep, every C250 is 254 mm and every C150 is 152 mm, because the sections are made to imperial dimensions. The second number changes with weight: within one depth, the heavier sections have a thicker web and slightly wider flanges, while the depth stays the same.

Beams follow the same logic. If you want the long version of why the numbers look odd, our guide to reading steel beam sizes explains it for W-shapes.

How to measure a channel you already have

Renovations, repairs and matching existing steel all start with identifying a channel that has no label. Here's how:

1. Measure the depth across the back of the web, from the outside of one flange to the outside of the other. This tells you the family: 152 mm is a C150, 203 mm is a C200, 254 mm is a C250, 305 mm is a C310, 381 mm is a C380.
2. Measure the flange width from the back of the web to the flange tip.
3. Measure the web thickness with a caliper at mid-depth, away from the fillets. This is the most reliable way to tell weights apart.
4. Check the flange. A sloped inside face points to a standard C. Parallel flanges with a sharp bend radius and uniform thin wall point to a cold-formed section, not a hot-rolled channel.
5. Match to the table. Find the depth family, then the weight whose web thickness and flange width are closest.

Here's what that looks like for three common families, using values from the CISC section tables (rounded):

Notice the pattern: in the C250 family the web nearly triples from the lightest to the heaviest section, but the flange grows by only 11 mm. If your measured web is between two table values, paint, mill scale and rust are the likely reasons; pick the nearest and have the designer confirm before relying on it.

Old buildings can contain channels rolled to discontinued sizes. If nothing matches well, give the measurements to your engineer rather than forcing a match.

Converting metric and imperial channel sizes

Most channels sold in Canada are the same physical sections as US channels, with two names. To convert:

• Depth: millimetres divided by 25.4 gives inches. Round to the family: 203 mm is 8 in, 254 mm is 10 in.
• Mass: kg/m divided by about 1.488 gives lb/ft, and lb/ft times 1.488 gives kg/m.

Worked example: C250x30. 254 mm is 10 inches, and 30.0 kg/m divided by 1.488 is about 20.2 lb/ft. The imperial name is C10x20; the small difference is rounding in the metric name. Going the other way, a C8x11.5 is 11.5 x 1.488, about 17.1 kg/m, so C200x17.

Our C-channel weight per metre post has the full list of equivalents and shows how to estimate the weight of an order.

Names that aren't hot-rolled C-channels

A few products get called "C-channel" but follow different naming:

• Cold-formed C-sections. Steel studs, joists and purlins are bent from sheet. North American steel stud names typically combine depth, member type, flange width and thickness in one code (for example 362S162-54), and they are never named by kg/m. A cold-formed C with the same outside size as a C200 is a much lighter member. See C-channel vs purlins and Z-channel.
• U-channel. Usually a light bent or extruded section, sometimes aluminium, not a structural C.
• Strut channel. Slotted framing channel for mechanical and electrical supports, named by its maker's part numbers.
• PFC. The UK term for a parallel flange channel; UK sizes don't map one-to-one to Canadian C-channels.

If a drawing says C200x17, it means the hot-rolled channel and nothing else.

Ordering channel by the right name

When you order, give the full designation from the drawing, the length and quantity, and any holes, copes or welded plates. If you have only a measurement from site, send the depth, flange width and web thickness and we'll help match it. Send drawings or a list through our quote form; we cut, drill and weld channels to your shop drawings, prime or galvanize to suit and deliver across the GTA and Ontario. See our steel products for what we supply.