Wide Flange Beam Sizes Explained
How to read a W-shape callout, why nominal depth is not actual depth, and what the 273 wide flange shapes actually cover.
The wide flange is the workhorse of structural steel. It shows up as beams, columns, headers and posts, and it is the shape most people mean when they say "I-beam" — which is a different shape entirely, but that argument is lost.
There are 273 wide flange shapes in standard use, spread across 17 nominal depth groups from W4 up to W44. This is how to read them.
Reading the callout
W21X50 means a wide flange, nominally 21 inches deep, weighing 50 pounds per foot.
That is the whole convention. The second number is always weight per foot, which is why a takeoff can be run straight off the drawing callouts without looking anything up — multiply the weight by the length and you have the piece.
A 40-foot W21X50 weighs 50 × 40 = 2,000 lb.
The same rule holds for M, S and HP shapes. It does not hold for angles or HSS, where the numbers are dimensions and the weight has to be looked up.
Nominal depth is not actual depth
This is the part that catches people, and it catches them at fit-up rather than at the desk.
Every shape in a group carries the same nominal depth in its name, but the actual depth varies — sometimes enormously — because heavier members in a group are rolled with thicker flanges. The rolling mill holds the inside distance between flanges constant and adds material outward.
The W14 group makes the point better than any explanation:
| Shapes in the W14 group | 36 |
| Weight range | 22 to 730 lb/ft |
| Actual depth range | 13.7 in to 22.4 in |
A W14X730 is called a fourteen-inch shape and measures 22.4 inches deep. That is over eight inches of difference inside a single group.
It is not unique to W14:
| Group | Shapes | Weight range (lb/ft) | Actual depth (in) |
|---|---|---|---|
| W8 | 13 | 10 – 67 | 7.9 – 9.0 |
| W12 | 29 | 14 – 336 | 11.9 – 16.8 |
| W14 | 36 | 22 – 730 | 13.7 – 22.4 |
| W21 | 18 | 44 – 201 | 20.6 – 23.0 |
| W24 | 21 | 55 – 370 | 23.6 – 28.0 |
| W36 | 21 | 135 – 652 | 35.6 – 41.1 |
| W44 | 4 | 230 – 335 | 42.9 – 44.0 |
Use the detailing dimension for anything that has to fit. The nominal number is a filing label, not a measurement.
Notice also that the heavy end of W12 and W14 overlaps the light end of much deeper groups. Those are column sections — nearly square, with flanges as wide as the section is deep — rather than beams. A W14X730 is not a deep beam; it is a very heavy column.
Which groups are actually used for what
Broadly, and with the caveat that the engineer decides:
- W4 – W10 — light framing, posts, joists, small headers
- W12 – W14 — the column groups. Wide flanges nearly as wide as they are deep, which is what you want in compression
- W16 – W24 — the everyday beam range for commercial floor framing
- W27 – W36 — long spans, transfer girders, heavy loads
- W40 – W44 — 4 shapes at the top of W44. Long-span roof and transfer work, and rarely stocked
What the numbers do not tell you
A callout gives you depth, weight, and by inference the group. It does not give you flange width, web or flange thickness, or any section property — and two shapes in the same group with similar weights can have quite different proportions.
For fit-up, connection design or anything structural, work from the detailing dimensions and the current AISC Steel Construction Manual. A designation is for ordering and estimating.
Look it up
- Structural shape weights — all 273 wide flange shapes plus channel, angle, HSS and pipe, with weight per foot, depth and area, and piece weight for any length and count
- Steel drawing symbols and abbreviations — how the rest of the callouts on the sheet read
- How to calculate steel beam weight — the arithmetic, and where it goes wrong