W21x73 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W21x73 is an American wide-flange beam 21.2 inches (538.5 mm) deep with a 8.3 in (210.8 mm) flange, weighing 73 pounds per foot (108.6 kg/m) — that is what the "73" 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 | 21.2 in (538.5 mm) |
| Flange width bf | 8.3 in (210.8 mm) |
| Web thickness tw | 0.455 in (11.6 mm) |
| Flange thickness tf | 0.74 in (18.8 mm) |
Weight & Cross-Section
| Weight per foot | 73 lb/ft (108.6 kg/m) |
| 20 ft bar | 1,460 lb |
| 40 ft bar | 2,920 lb |
| Area A | 21.5 in² (138.7 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 1,600 in⁴ (66,597 cm⁴) |
| Section modulus Sx | 151 in³ (2,474 cm³) |
| Radius of gyration rx | 8.64 in |
| Moment of inertia Iy | 70.6 in⁴ (2,939 cm⁴) |
| Section modulus Sy | 17 in³ (279 cm³) |
| Radius of gyration ry | 1.81 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W21x68 | 21.1 × 8.27 | 68 | 1,480 | 140 | −7 % | −7 % |
| W21x73 (this page) | 21.2 × 8.3 | 73 | 1,600 | 151 | — | — |
| W21x83 | 21.4 × 8.36 | 83 | 1,830 | 171 | +14 % | +14 % |
Deflection example
A simply supported W21x73 spanning 34 ft with a 10 kip point load at midspan deflects 0.31 in (E = 29,000 ksi, Ix = 1,600 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 W21x73 beam weigh?
W21x73 weighs 73 pounds per foot (108.6 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 1,460 lb and a 40 ft bar 2,920 lb.
What are the dimensions of a W21x73?
W21x73 is 21.2 in (538.5 mm) deep with a 8.3 in (210.8 mm) wide flange. The web is 0.46 in thick and the flanges are 0.74 in thick. Note the actual depth differs from the nominal W21 label — always design with the actual value.
What are the dimensions of a W21x73 in mm?
W21x73 is 538.5 mm deep with a 210.8 mm wide flange; the web is 11.6 mm and the flange 18.8 mm thick. In metric section properties: Ix = 66,597 cm⁴, Sx = 2,474 cm³.
How much does a W21x73 weigh in kg?
108.6 kg per meter. A 6 m bar weighs 652 kg and a 12 m bar 1,304 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W21x73?
About the strong axis, Ix = 1,600 in⁴ (66,597 cm⁴) with section modulus Sx = 151 in³. About the weak axis, Iy = 70.6 in⁴ and Sy = 17 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W21x73 or W21x83 — what does one size up change?
W21x83 is about 14% heavier (83 vs 73 lb/ft) but about 14% stiffer (Ix 1,830 vs 1,600 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