W21x57 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W21x57 is an American wide-flange beam 21.1 inches (535.9 mm) deep with a 6.56 in (166.6 mm) flange, weighing 57 pounds per foot (84.8 kg/m) — that is what the "57" 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 | 21.1 in (535.9 mm) |
| Flange width bf | 6.56 in (166.6 mm) |
| Web thickness tw | 0.405 in (10.3 mm) |
| Flange thickness tf | 0.65 in (16.5 mm) |
Weight & Cross-Section
| Weight per foot | 57 lb/ft (84.8 kg/m) |
| 20 ft bar | 1,140 lb |
| 40 ft bar | 2,280 lb |
| Area A | 16.7 in² (107.7 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 1,170 in⁴ (48,699 cm⁴) |
| Section modulus Sx | 111 in³ (1,819 cm³) |
| Radius of gyration rx | 8.36 in |
| Moment of inertia Iy | 30.6 in⁴ (1,274 cm⁴) |
| Section modulus Sy | 9.35 in³ (153 cm³) |
| Radius of gyration ry | 1.35 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W21x50 | 20.8 × 6.53 | 50 | 984 | 94.5 | −12 % | −16 % |
| W21x57 (this page) | 21.1 × 6.56 | 57 | 1,170 | 111 | — | — |
| W21x62 | 21 × 8.24 | 62 | 1,330 | 127 | +9 % | +14 % |
Deflection example
A simply supported W21x57 spanning 34 ft with a 10 kip point load at midspan deflects 0.42 in (E = 29,000 ksi, Ix = 1,170 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 W21x57 beam weigh?
W21x57 weighs 57 pounds per foot (84.8 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 1,140 lb and a 40 ft bar 2,280 lb.
What are the dimensions of a W21x57?
W21x57 is 21.1 in (535.9 mm) deep with a 6.56 in (166.6 mm) wide flange. The web is 0.41 in thick and the flanges are 0.65 in thick. Note the actual depth differs from the nominal W21 label — always design with the actual value.
What are the dimensions of a W21x57 in mm?
W21x57 is 535.9 mm deep with a 166.6 mm wide flange; the web is 10.3 mm and the flange 16.5 mm thick. In metric section properties: Ix = 48,699 cm⁴, Sx = 1,819 cm³.
How much does a W21x57 weigh in kg?
84.8 kg per meter. A 6 m bar weighs 509 kg and a 12 m bar 1,018 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W21x57?
About the strong axis, Ix = 1,170 in⁴ (48,699 cm⁴) with section modulus Sx = 111 in³. About the weak axis, Iy = 30.6 in⁴ and Sy = 9.35 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W21x57 or W21x62 — what does one size up change?
W21x62 is about 9% heavier (62 vs 57 lb/ft) but about 14% stiffer (Ix 1,330 vs 1,170 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