W21x50 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W21x50 is an American wide-flange beam 20.8 inches (528.3 mm) deep with a 6.53 in (165.9 mm) flange, weighing 50 pounds per foot (74.4 kg/m) — that is what the "50" 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 | 20.8 in (528.3 mm) |
| Flange width bf | 6.53 in (165.9 mm) |
| Web thickness tw | 0.38 in (9.7 mm) |
| Flange thickness tf | 0.535 in (13.6 mm) |
Weight & Cross-Section
| Weight per foot | 50 lb/ft (74.4 kg/m) |
| 20 ft bar | 1,000 lb |
| 40 ft bar | 2,000 lb |
| Area A | 14.7 in² (94.8 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 984 in⁴ (40,957 cm⁴) |
| Section modulus Sx | 94.5 in³ (1,549 cm³) |
| Radius of gyration rx | 8.18 in |
| Moment of inertia Iy | 24.9 in⁴ (1,036 cm⁴) |
| Section modulus Sy | 7.64 in³ (125 cm³) |
| Radius of gyration ry | 1.3 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W21x44 | 20.7 × 6.5 | 44 | 843 | 81.6 | −12 % | −14 % |
| W21x50 (this page) | 20.8 × 6.53 | 50 | 984 | 94.5 | — | — |
| W21x57 | 21.1 × 6.56 | 57 | 1,170 | 111 | +14 % | +19 % |
Deflection example
A simply supported W21x50 spanning 33 ft with a 10 kip point load at midspan deflects 0.45 in (E = 29,000 ksi, Ix = 984 in⁴). The L/360 serviceability limit for this span is 1.1 in — the shape passes this quick check.
Calculate with your own span and load →
Frequently asked questions
How much does a W21x50 beam weigh?
W21x50 weighs 50 pounds per foot (74.4 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 1,000 lb and a 40 ft bar 2,000 lb.
What are the dimensions of a W21x50?
W21x50 is 20.8 in (528.3 mm) deep with a 6.53 in (165.9 mm) wide flange. The web is 0.38 in thick and the flanges are 0.54 in thick. Note the actual depth differs from the nominal W21 label — always design with the actual value.
What are the dimensions of a W21x50 in mm?
W21x50 is 528.3 mm deep with a 165.9 mm wide flange; the web is 9.7 mm and the flange 13.6 mm thick. In metric section properties: Ix = 40,957 cm⁴, Sx = 1,549 cm³.
How much does a W21x50 weigh in kg?
74.4 kg per meter. A 6 m bar weighs 446 kg and a 12 m bar 893 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W21x50?
About the strong axis, Ix = 984 in⁴ (40,957 cm⁴) with section modulus Sx = 94.5 in³. About the weak axis, Iy = 24.9 in⁴ and Sy = 7.64 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W21x50 or W21x57 — what does one size up change?
W21x57 is about 14% heavier (57 vs 50 lb/ft) but about 19% stiffer (Ix 1,170 vs 984 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