W18×50 vs W21×50
A side-by-side comparison of two AISC wide-flange beams, 16th Edition. Detailing dimensions to the nearest 1/16 in.
W18×50 and W21×50 both weigh 50 lb per foot, so the choice comes down to depth and stiffness rather than weight.
W21×50 is the deeper section at a nominal 21 in., versus 18 in.
W21×50 has the greater bending strength: section modulus Sx of 94.5 in³ versus 88.9, about 6% more.
| Property | W18×50 | W21×50 |
|---|---|---|
| Weight | 50 lb/ft | 50 lb/ft |
| Depth (d) | 18" | 20 7/8" |
| Flange width (bf) | 7 1/2" | 6 1/2" |
| Web thickness (tw) | 3/8" | 3/8" |
| Flange thickness (tf) | 9/16" | 9/16" |
| Area (A) | 14.7 in² | 14.7 in² |
| Moment of inertia (Ix) | 800 in⁴ | 984 in⁴ |
| Section modulus (Sx) | 88.9 in³ | 94.5 in³ |
| Plastic modulus (Zx) | 101 in³ | 110 in³ |
Open W18×50 in the interactive size chart →
Full detail: W18×50 · W21×50. Verify critical dimensions against the current AISC Steel Construction Manual before fabrication.
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