W8×40 vs W12×40
A side-by-side comparison of two AISC wide-flange beams, 16th Edition. Detailing dimensions to the nearest 1/16 in.
W8×40 and W12×40 both weigh 40 lb per foot, so the choice comes down to depth and stiffness rather than weight.
W12×40 is the deeper section at a nominal 12 in., versus 8 in.
W12×40 has the greater bending strength: section modulus Sx of 51.5 in³ versus 35.5, about 45% more.
| Property | W8×40 | W12×40 |
|---|---|---|
| Weight | 40 lb/ft | 40 lb/ft |
| Depth (d) | 8 1/4" | 12" |
| Flange width (bf) | 8 1/8" | 8" |
| Web thickness (tw) | 3/8" | 5/16" |
| Flange thickness (tf) | 9/16" | 1/2" |
| Area (A) | 11.7 in² | 11.7 in² |
| Moment of inertia (Ix) | 146 in⁴ | 307 in⁴ |
| Section modulus (Sx) | 35.5 in³ | 51.5 in³ |
| Plastic modulus (Zx) | 39.8 in³ | 57 in³ |
Open W8×40 in the interactive size chart →
Full detail: W8×40 · W12×40. Verify critical dimensions against the current AISC Steel Construction Manual before fabrication.
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