W18x40 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W18x40 is an American wide-flange beam 17.9 inches (454.7 mm) deep with a 6.02 in (152.9 mm) flange, weighing 40 pounds per foot (59.5 kg/m) — that is what the "40" 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 | 17.9 in (454.7 mm) |
| Flange width bf | 6.02 in (152.9 mm) |
| Web thickness tw | 0.315 in (8 mm) |
| Flange thickness tf | 0.525 in (13.3 mm) |
Weight & Cross-Section
| Weight per foot | 40 lb/ft (59.5 kg/m) |
| 20 ft bar | 800 lb |
| 40 ft bar | 1,600 lb |
| Area A | 11.8 in² (76.1 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 612 in⁴ (25,473 cm⁴) |
| Section modulus Sx | 68.4 in³ (1,121 cm³) |
| Radius of gyration rx | 7.21 in |
| Moment of inertia Iy | 19.1 in⁴ (795 cm⁴) |
| Section modulus Sy | 6.35 in³ (104 cm³) |
| Radius of gyration ry | 1.27 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W18x35 | 17.7 × 6 | 35 | 510 | 57.6 | −12 % | −17 % |
| W18x40 (this page) | 17.9 × 6.02 | 40 | 612 | 68.4 | — | — |
| W18x46 | 18.1 × 6.06 | 46 | 712 | 78.8 | +15 % | +16 % |
Deflection example
A simply supported W18x40 spanning 29 ft with a 10 kip point load at midspan deflects 0.5 in (E = 29,000 ksi, Ix = 612 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 W18x40 beam weigh?
W18x40 weighs 40 pounds per foot (59.5 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 800 lb and a 40 ft bar 1,600 lb.
What are the dimensions of a W18x40?
W18x40 is 17.9 in (454.7 mm) deep with a 6.02 in (152.9 mm) wide flange. The web is 0.32 in thick and the flanges are 0.53 in thick. Note the actual depth differs from the nominal W18 label — always design with the actual value.
What are the dimensions of a W18x40 in mm?
W18x40 is 454.7 mm deep with a 152.9 mm wide flange; the web is 8 mm and the flange 13.3 mm thick. In metric section properties: Ix = 25,473 cm⁴, Sx = 1,121 cm³.
How much does a W18x40 weigh in kg?
59.5 kg per meter. A 6 m bar weighs 357 kg and a 12 m bar 714 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W18x40?
About the strong axis, Ix = 612 in⁴ (25,473 cm⁴) with section modulus Sx = 68.4 in³. About the weak axis, Iy = 19.1 in⁴ and Sy = 6.35 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W18x40 or W18x46 — what does one size up change?
W18x46 is about 15% heavier (46 vs 40 lb/ft) but about 16% stiffer (Ix 712 vs 612 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