W8x31 weight and dimensions
46.1 kg/m · 31.00 lb/ft
W8x31 is a 203 mm deep beam with a 203 mm flange, 7.24 mm web and 11 mm flange thickness. It weighs 46.1 kg per metre (31.00 lb/ft). It belongs to the W-shape wide flange beam series, American (AISC / ASTM A6).
W8x31 weight calculator
Weight of standard lengths
| Pieces | 20 ft each (lb) | 40 ft each (lb) |
|---|---|---|
| 1 | 619.6 | 1,239.1 |
| 5 | 3,097.8 | 6,195.6 |
| 10 | 6,195.6 | 12,391.1 |
| 20 | 12,391.1 | 24,782.2 |
| 50 | 30,977.8 | 61,955.5 |
Pieces per ton
| 20 ft lengths per short ton (2,000 lb) | 3.2 |
| 40 ft lengths per short ton (2,000 lb) | 1.6 |
| Length per ton | 64.6 ft |
Useful for converting a tonnage order into a number of bars.
Surface area for painting
| Per metre of length | 1.190 m²/m |
| Per foot of length | 3.90 ft²/ft |
| Per tonne of steel | 25.8 m²/t |
| A 12 m length | 14.28 m² |
Outside perimeter × length, all faces (AISC perimeter PB). Use it to estimate paint, primer, fireproofing or galvanizing quantities.
Cross-section
Drawn to scale. Dimensions in mm.
Dimensions
| Depth h | 203 mm | 7.992 in |
| Flange width b | 203 mm | 7.992 in |
| Web thickness tw | 7.24 mm | 0.285 in |
| Flange thickness tf | 11 mm | 0.433 in |
| Root radius r | 10.1 mm | 0.398 in |
| Mass | 46.1 kg/m | 31.00 lb/ft |
Section properties
| Property | Value | Unit |
|---|---|---|
| Area | 58.90 | cm² |
| Moment of inertia Ix | 4,580 | cm⁴ |
| Moment of inertia Iy | 1,540 | cm⁴ |
| Elastic modulus Zx | 451 | cm³ |
| Elastic modulus Zy | 152 | cm³ |
| Plastic modulus Zpx | 498 | cm³ |
| Plastic modulus Zpy | 231 | cm³ |
| Radius of gyration rx | 8.81 | cm |
| Radius of gyration ry | 5.13 | cm |
| Torsion constant J | 22.30 | cm⁴ |
Equivalent sections in other standards
The closest sections by depth and weight. They are not direct substitutes: check bending, buckling and connection details before swapping one for another.
W8x31 and its closest equivalents, drawn over each other at the same scale.
| Section | Standard | Depth (mm) | kg/m | Weight vs W8x31 |
|---|---|---|---|---|
| W8x31 | AISC | 203 | 46.1 | — |
| ISWB 200 (203 x 152, 52.09 kg/m) | IS | 203 | 52.09 | +13.0% |
| ISWB 225 | IS | 225 | 33.93 | -26.4% |
| HEA 220 | EN | 210 | 50.51 | +9.6% |
| HEA 200 | EN | 190 | 42.26 | -8.3% |
W8 series weights
Next lighter: W8x28 (41.7 kg/m). Next heavier: W8x35 (52 kg/m).
Stiffness and strength per kilogram
The elastic section modulus Zx governs bending strength. Dividing it by the weight shows how efficiently each size uses its steel: higher is better when weight is the cost driver.
| Section | kg/m | Ix (cm⁴) | Zx (cm³) | Zx per kg/m |
|---|---|---|---|---|
| W8x21 | 31.30 | 3,130 | 298.0 | 9.52 |
| W8x24 | 35.90 | 3,440 | 342.0 | 9.53 |
| W8x28 | 41.70 | 4,080 | 398.0 | 9.54 |
| W8x31 | 46.10 | 4,580 | 451.0 | 9.78 |
| W8x35 | 52.00 | 5,290 | 511.0 | 9.83 |
| W8x40 | 59.00 | 6,080 | 582.0 | 9.86 |
| W8x48 | 71.00 | 7,660 | 708.0 | 9.97 |
Full table: W-shape (wide flange) beam chart (PDF).
How the weight is calculated
Mass per metre = cross-sectional area × density of steel = 58.90 cm² × 0.785 kg/(cm²·m) = 46.24 kg/m.
Rolled sections are made to a nominal mass, and the actual mass can differ by a few percent within the tolerances of ASTM A6. For purchasing, invoicing by weight or checking deliveries, use the producer's stated mass.
Typical uses
Wide flange sections like this are used as columns, heavy beams and transfer girders, where stiffness about both axes matters.
Frequently asked questions
What is the weight of W8x31 per metre?
W8x31 weighs 46.1 kg/m, which is 31.00 lb/ft.
How much does a 6 m or 12 m length of W8x31 weigh?
A 6 m length weighs about 276.6 kg and a 12 m length about 553.2 kg.
What is the equivalent of W8x31 in other standards?
By depth and weight the closest match is ISWB 200 (203 x 152, 52.09 kg/m) (52.09 kg/m, 203 mm deep). Check section properties before substituting one for the other.
Source: AISC Shapes Database v16.0. Values are nominal; verify with the producer before ordering.