W18x258 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W18x258 is an American wide-flange beam 21.5 inches (546.1 mm) deep with a 11.8 in (299.7 mm) flange, weighing 258 pounds per foot (384 kg/m) — that is what the "258" in the designation means. All values below are the standard AISC published section properties used in US structural design, with metric equivalents alongside.
Typical uses: floor and roof framing, columns, headers, and general steel construction. For a quick stiffness check, see the deflection example below or open the beam calculator with your own span and load.
Dimensions
| Depth d | 21.5 in (546.1 mm) |
| Flange width bf | 11.8 in (299.7 mm) |
| Web thickness tw | 1.28 in (32.5 mm) |
| Flange thickness tf | 2.3 in (58.4 mm) |
Weight & Cross-Section
| Weight per foot | 258 lb/ft (384 kg/m) |
| 20 ft bar | 5,160 lb |
| 40 ft bar | 10,320 lb |
| Area A | 76 in² (490.3 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 5,510 in⁴ (229,343 cm⁴) |
| Section modulus Sx | 514 in³ (8,423 cm³) |
| Radius of gyration rx | 8.53 in |
| Moment of inertia Iy | 628 in⁴ (26,139 cm⁴) |
| Section modulus Sy | 107 in³ (1,753 cm³) |
| Radius of gyration ry | 2.88 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W18x234 | 21.1 × 11.7 | 234 | 4,900 | 466 | −9 % | −11 % |
| W18x258 (this page) | 21.5 × 11.8 | 258 | 5,510 | 514 | — | — |
| W18x283 | 21.9 × 11.9 | 283 | 6,170 | 565 | +10 % | +12 % |
Deflection example
A simply supported W18x258 spanning 34 ft with a 10 kip point load at midspan deflects 0.09 in (E = 29,000 ksi, Ix = 5,510 in⁴). The L/360 serviceability limit for this span is 1.13 in — the shape passes this quick check.
Calculate with your own span and load →
Frequently asked questions
How much does a W18x258 beam weigh?
W18x258 weighs 258 pounds per foot (384 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 5,160 lb and a 40 ft bar 10,320 lb.
What are the dimensions of a W18x258?
W18x258 is 21.5 in (546.1 mm) deep with a 11.8 in (299.7 mm) wide flange. The web is 1.28 in thick and the flanges are 2.3 in thick. Note the actual depth differs from the nominal W18 label — always design with the actual value.
What are the dimensions of a W18x258 in mm?
W18x258 is 546.1 mm deep with a 299.7 mm wide flange; the web is 32.5 mm and the flange 58.4 mm thick. In metric section properties: Ix = 229,343 cm⁴, Sx = 8,423 cm³.
How much does a W18x258 weigh in kg?
384 kg per meter. A 6 m bar weighs 2,304 kg and a 12 m bar 4,607 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W18x258?
About the strong axis, Ix = 5,510 in⁴ (229,343 cm⁴) with section modulus Sx = 514 in³. About the weak axis, Iy = 628 in⁴ and Sy = 107 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W18x258 or W18x283 — what does one size up change?
W18x283 is about 10% heavier (283 vs 258 lb/ft) but about 12% stiffer (Ix 6,170 vs 5,510 in⁴). Going one step up within the same depth group is usually the cheapest way to cut deflection.
Values are entered from the governing standard’s published tables and cross-checked programmatically against its mass and section formulas before publication. Spotted an error? Write to advertising@metalabout.net — verified corrections ship within days. About