How to Read a Wide Flange Beam Designation (W8x31, W12x26, etc.)
A structural drawing calls for a W12x26, and the purchase order goes out today. If you are new to structural steel, that string of letters and numbers can slow you down. Every wide flange beam designation follows the same pattern, so once you know it, you can read any W beam size on a drawing or mill list. This guide breaks down what each part of the designation means, where new engineers and buyers get tripped up, and how to use the numbers when you order.
The three parts of a wide flange beam designation
Take W8x31 as an example. The American Institute of Steel Construction defines the W shape designation as the nominal depth in inches followed by the weight per foot in pounds. Read left to right, it tells you:
- W: The shape. W stands for wide flange, the H-shaped profile with wide, parallel flanges on each side of the web.
- 8: The nominal depth, about 8 inches from the outside of the top flange to the outside of the bottom flange.
- 31: The weight, 31 pounds per linear foot of beam.
So a W12x26 is a wide flange beam in the 12-inch depth group that weighs 26 pounds per foot. The “x” is a separator, read as “by,” as in “W12 by 26.”
Nominal depth is a size group, not an exact measurement
The first number names a family of sections. It is not a tape-measure reading. Published dimensions for a W12x26 show an actual depth of 12.2 inches and a flange width of 6.49 inches.
The gap grows as sections get heavier. Within a depth group, the clear distance between the flanges stays roughly the same, so added weight goes into thicker flanges and a thicker web, which pushes the overall depth up. At the far end of the W14 group, a W14x730 measures 22.4 inches deep with a flange almost 18 inches wide.
When fit-up, clearances, or connections matter, check the actual depth, flange width, and web and flange thickness in a shape table.
Same depth group, very different beams
Two beams with the same first number can perform very differently. A W8x31 has flanges about as wide as the beam is deep, a proportion often chosen for columns. A lighter W8 has narrower, thinner flanges and carries less load. Always confirm the full designation, not just the depth.
How to use weight per foot when you order
The second number is the one buyers use most. Multiply it by the length to get an estimated beam weight:
- A W12x26 at 20 feet weighs about 520 pounds (26 x 20).
- A W8x31 at 40 feet weighs about 1,240 pounds (31 x 40).
That figure feeds freight planning, crane and forklift selection, and pricing, since structural steel is often priced by weight. If two sections meet the engineer’s requirements, the lighter one usually costs less to buy, ship, and handle.
If your drawings call for beams in specific lengths, cut-to-length services let you order sections ready for fit-up instead of trimming them on site.
Other designations you will see on drawings
W shapes are not the only beams on a structural set. A few other prefixes follow the same depth-by-weight format:
- S: American Standard beams, the classic I-beams with narrower, tapered flanges.
- M: Miscellaneous shapes that do not fit the W or S groups.
- HP: Bearing piles, with flanges and web of nearly equal thickness.
- C: Standard channels, with a C-shaped profile.
You may also see metric designations on international projects. These list depth in millimeters and mass in kilograms per meter, so a W8x31 appears as W200x46.1 and a W12x26 as W310x38.7.
Steel grade is not part of the designation. It appears in the general notes or the bill of materials. ASTM A992 is the grade most often specified for wide flange beams, with A36, A572, and others used when a project calls for them. For more on W and S shapes, see our guide on the difference between wide flange beams and I-beams.
Where they excel is in applications with concentrated loads and shear demands, such as monorails, crane runways, and machine bases, where the thicker web carries vertical force efficiently. Working with experienced steel I-beam suppliers ensures you get the correct S-section for specialized loads.
Need help matching a designation to the right beam?
Saginaw Pipe is a wide flange beam supplier with section depths from 4 to 44 inches and weights from 9 to 730 pounds per foot, plus in-house saw cutting, torch cutting, and blasting. Send us the sizes from your drawings and our team will confirm availability, grade, and lengths. Request a quote or call 1.800.433.1374.
Frequently Asked Questions
What does W8x31 mean?
W8x31 is a wide flange beam with a nominal depth of 8 inches that weighs 31 pounds per linear foot. The W identifies the wide flange shape, the 8 is the depth group, and the 31 is the weight.
Is a W12 beam exactly 12 inches deep?
Not always. The 12 is a nominal depth that names a size group, and the actual depth changes with the weight of the section. A W12x26, for example, is 12.2 inches deep, so check a shape table when exact dimensions matter.
How do I calculate the weight of a wide flange beam?
Multiply the second number in the designation by the beam length in feet. A W12x26 that is 20 feet long weighs about 520 pounds.
What is the difference between a W beam and an S beam?
A W beam has wide flanges with parallel inner and outer faces, while an S beam, or American Standard I-beam, has narrower flanges with a sloped inner face. Both use the same depth-by-weight designation format.
Conclusion
Every wide flange beam designation follows the same pattern: the W for the shape, the nominal depth in inches, and the weight in pounds per linear foot. Once you know that, a W8x31 or W12x26 on a drawing tells you what family the beam belongs to and roughly what it will weigh on the truck. Treat the depth as a size group, not an exact measurement, and check a shape table when fit-up or clearances matter. Use the weight per foot to estimate freight, handling, and cost, and confirm the steel grade in the project notes, since it is not part of the designation.
