W18x55 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W18x55 is an American wide-flange beam 18.1 inches (459.7 mm) deep with a 7.53 in (191.3 mm) flange, weighing 55 pounds per foot (81.9 kg/m) — that is what the "55" 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 | 18.1 in (459.7 mm) |
| Flange width bf | 7.53 in (191.3 mm) |
| Web thickness tw | 0.39 in (9.9 mm) |
| Flange thickness tf | 0.63 in (16 mm) |
Weight & Cross-Section
| Weight per foot | 55 lb/ft (81.9 kg/m) |
| 20 ft bar | 1,100 lb |
| 40 ft bar | 2,200 lb |
| Area A | 16.2 in² (104.5 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 890 in⁴ (37,044 cm⁴) |
| Section modulus Sx | 98.3 in³ (1,611 cm³) |
| Radius of gyration rx | 7.41 in |
| Moment of inertia Iy | 44.9 in⁴ (1,869 cm⁴) |
| Section modulus Sy | 11.9 in³ (195 cm³) |
| Radius of gyration ry | 1.67 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W18x50 | 18 × 7.5 | 50 | 800 | 88.9 | −9 % | −10 % |
| W18x55 (this page) | 18.1 × 7.53 | 55 | 890 | 98.3 | — | — |
| W18x60 | 18.2 × 7.56 | 60 | 984 | 108 | +9 % | +11 % |
Deflection example
A simply supported W18x55 spanning 29 ft with a 10 kip point load at midspan deflects 0.34 in (E = 29,000 ksi, Ix = 890 in⁴). The L/360 serviceability limit for this span is 0.97 in — the shape passes this quick check.
Calculate with your own span and load →
Frequently asked questions
How much does a W18x55 beam weigh?
W18x55 weighs 55 pounds per foot (81.9 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 1,100 lb and a 40 ft bar 2,200 lb.
What are the dimensions of a W18x55?
W18x55 is 18.1 in (459.7 mm) deep with a 7.53 in (191.3 mm) wide flange. The web is 0.39 in thick and the flanges are 0.63 in thick. Note the actual depth differs from the nominal W18 label — always design with the actual value.
What are the dimensions of a W18x55 in mm?
W18x55 is 459.7 mm deep with a 191.3 mm wide flange; the web is 9.9 mm and the flange 16 mm thick. In metric section properties: Ix = 37,044 cm⁴, Sx = 1,611 cm³.
How much does a W18x55 weigh in kg?
81.9 kg per meter. A 6 m bar weighs 491 kg and a 12 m bar 982 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W18x55?
About the strong axis, Ix = 890 in⁴ (37,044 cm⁴) with section modulus Sx = 98.3 in³. About the weak axis, Iy = 44.9 in⁴ and Sy = 11.9 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W18x55 or W18x60 — what does one size up change?
W18x60 is about 9% heavier (60 vs 55 lb/ft) but about 11% stiffer (Ix 984 vs 890 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