W8x31 is a wide flange steel beam that is 8 in deep with an 8 in flange and weighs 31 lb/ft (46.1 kg/m). Its metric designation is W200x46.1. All values below come from the AISC Shapes Database v16.0.
W8x31 Dimensions
| Property | Symbol | Imperial | Metric |
|---|---|---|---|
| Nominal weight | W | 31 lb/ft | 46.1 kg/m |
| Cross-sectional area | A | 9.13 in² | 5,890 mm² |
| Depth | d | 8 in | 203 mm |
| Flange width | bf | 8 in | 203 mm |
| Web thickness | tw | 0.285 in | 7.24 mm |
| Flange thickness | tf | 0.435 in | 11 mm |
| Distance to web toe of fillet (design) | kdes | 0.829 in | 21.1 mm |
| Distance to web toe of fillet (detailing) | kdet | 1.125 in | 28.6 mm |
| Web center line to flange toe of fillet | k1 | 0.75 in | 19.1 mm |
| Distance between web toes of fillets | T | 5.75 in | 146 mm |
| Workable gage (inner holes) | WGi | 5.5 in | 140 mm |
W8x31 Section Properties
| Property | Symbol | Imperial | Metric |
|---|---|---|---|
| Moment of inertia, x-axis | Ix | 110 in⁴ | 45.8 ×10⁶ mm⁴ |
| Elastic section modulus, x-axis | Sx | 27.5 in³ | 451 ×10³ mm³ |
| Plastic section modulus, x-axis | Zx | 30.4 in³ | 498 ×10³ mm³ |
| Radius of gyration, x-axis | rx | 3.47 in | 88.1 mm |
| Moment of inertia, y-axis | Iy | 37.1 in⁴ | 15.4 ×10⁶ mm⁴ |
| Elastic section modulus, y-axis | Sy | 9.27 in³ | 152 ×10³ mm³ |
| Plastic section modulus, y-axis | Zy | 14.1 in³ | 231 ×10³ mm³ |
| Radius of gyration, y-axis | ry | 2.02 in | 51.3 mm |
| Torsional constant | J | 0.536 in⁴ | 223 ×10³ mm⁴ |
| Warping constant | Cw | 530 in⁶ | 142 ×10⁹ mm⁶ |
| Effective radius of gyration | rts | 2.26 in | 57.4 mm |
| Distance between flange centroids | ho | 7.57 in | 192 mm |
| Flange slenderness | bf/2tf | 9.19 | 9.19 |
| Web slenderness | h/tw | 22.3 | 22.3 |
W8x31 Weight Calculator
Enter a length to get the total weight of a W8x31 beam. A 20 ft length weighs 620 lb.
Uses the AISC nominal weight: 31 lb/ft (46.1 kg/m).
Beams Similar to W8x31
See every W8 size in the W8 beam sizes chart, or compare all shapes in the wide flange beam sizes chart. Working in millimetres? W8x31 is listed as W200x46.1 in the metric wide flange beam sizes chart.
W8x31 FAQ
What does W8x31 mean?
W means wide flange. The first number (8) is the nominal depth in inches, and the second number (31) is the weight in pounds per foot. The actual depth of W8x31 is 8 in. How to read steel beam sizes.
How much does a W8x31 beam weigh?
W8x31 weighs 31 lb per foot (46.1 kg per meter). A 20 ft beam weighs about 620 lb. Use the calculator above for any length.
What is the metric equivalent of W8x31?
The metric (SI) designation is W200x46.1: 203 mm deep with a 203 mm flange and 46.1 kg/m.
How far can a W8x31 beam span?
Span depends on the load, support conditions, deflection limits and local building code, so it cannot be read from a size table. A licensed structural engineer must size any beam that carries a load.
Source: AISC Shapes Database v16.0, consistent with the AISC Steel Construction Manual, 16th Edition. Last updated: September 2026.
This page is reference information only and is not engineering advice. Do not use it for a specific design without verification by a licensed engineer or architect. Full disclaimer.