Short answer
W10x15 is an AISC wide-flange beam: W for wide flange, 10 for a nominal depth of 10 inches, and 15 for a weight of 15 pounds per linear foot. The "x" is read as "by". A 20 ft piece weighs about 300 lb.
Breaking it down
- W: wide-flange shape, an I-shaped section with flanges that are parallel on the inside and outside faces.
- 10: nominal depth in inches. The actual depth of a W10x15 is 9.99 in.
- 15: weight per foot in pounds. The flange is 4.00 in wide.
In metric terms, a W10x15 is 22.3 kg/m. You will see it written W10x15, W10X15 or W 10 x 15. They are the same section. The full dimension table is on the W10x15 page.
Why nominal depth is only nominal
A W10 family has many weights, and the actual depth changes slightly with weight because heavier sections have thicker flanges. W10x15 is 9.99 in deep; a heavier W10 is deeper than 10 in. So "10" tells you which family it belongs to, not an exact dimension. Never use the nominal depth for detailing or clearance checks. Use the table value.
The same rule applies to W12x26 (12.22 in actual depth) and W24x55 (23.57 in).
What else might follow the designation?
Drawings add information after the size. You may see:
- A length: W10x15 x 20'-0".
- Camber: W10x15 (C=3/4").
- Studs: W10x15 [24] meaning 24 shear studs.
- A grade: W10x15 A992.
- Quantities in a schedule, not in the label.
Knowing that the second number is weight also helps you sanity-check a callout. If a drawing says W10x150, it is probably a typo for W10x15 or a column size, and a quick look at the shape tables will tell you whether that size exists.
How do other families read?
Only some AISC families put the weight at the end. For HSS, angles and plates, the numbers are dimensions. See What do HSS, L, C, MC and PL designations mean?. For non-US sections, read What is the UK equivalent of a W-beam?.
When you upload a drawing to SteelFlo, designations in all these styles are found and normalized, so W10x15 and W10X15 count as one size.
The W10 family
A few W10 sizes from the tables, to show how weight and depth move together:
| Size | lb/ft | Actual depth |
|---|---|---|
| W10x12 | 12 | 9.87 in |
| W10x15 | 15 | 9.99 in |
| W10x22 | 22 | 10.17 in |
| W10x33 | 33 | 9.73 in |
| W10x49 | 49 | 9.98 in |
| W10x112 | 112 | 11.36 in |
Notice that depth does not rise steadily with weight, so you cannot infer depth from the weight number. Some lighter W10s are deeper than some heavier ones, because each rolling is built around different flange and web thicknesses.
How is W10x15 different from S, M, HP and WT?
AISC uses different letters for different families of I-shaped sections:
- W: wide flange, the common one.
- S: American standard beam, with tapered flanges. S12x31.8 is 12 in deep and 31.8 lb/ft.
- M: miscellaneous beam, a lighter grab bag of sections that are not W or S. M10x9 is 9 lb/ft.
- HP: bearing pile, with flange and web the same thickness. HP12x53 is 53 lb/ft.
- WT, ST, MT: structural tees cut from W, S or M shapes. WT6x25 is 25 lb/ft.
All of these read depth then weight per foot. The letter tells you the family, and the family tells you how the flange is shaped.
Does it matter if the drawing writes W10X15 or W10x15?
No. The capital X and lowercase x are the same. You will also see spaces (W 10 x 15) and sometimes a dash (W10-15) on older drawings. A good takeoff process, manual or automated, treats them as one size so the count is not split across spellings. SteelFlo normalizes the variants and lets you browse every size in the shape database.
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