W21x122 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W21x122 is an American wide-flange beam 21.7 inches (551.2 mm) deep with a 12.4 in (315 mm) flange, weighing 122 pounds per foot (181.6 kg/m) — that is what the "122" 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 | 21.7 in (551.2 mm) |
| Flange width bf | 12.4 in (315 mm) |
| Web thickness tw | 0.6 in (15.2 mm) |
| Flange thickness tf | 0.96 in (24.4 mm) |
Weight & Cross-Section
| Weight per foot | 122 lb/ft (181.6 kg/m) |
| 20 ft bar | 2,440 lb |
| 40 ft bar | 4,880 lb |
| Area A | 35.9 in² (231.6 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 2,960 in⁴ (123,204 cm⁴) |
| Section modulus Sx | 273 in³ (4,474 cm³) |
| Radius of gyration rx | 9.09 in |
| Moment of inertia Iy | 305 in⁴ (12,695 cm⁴) |
| Section modulus Sy | 49.2 in³ (806 cm³) |
| Radius of gyration ry | 2.92 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W21x111 | 21.5 × 12.3 | 111 | 2,670 | 249 | −9 % | −10 % |
| W21x122 (this page) | 21.7 × 12.4 | 122 | 2,960 | 273 | — | — |
| W21x132 | 21.8 × 12.4 | 132 | 3,220 | 295 | +8 % | +9 % |
Deflection example
A simply supported W21x122 spanning 35 ft with a 10 kip point load at midspan deflects 0.18 in (E = 29,000 ksi, Ix = 2,960 in⁴). The L/360 serviceability limit for this span is 1.17 in — the shape passes this quick check.
Calculate with your own span and load →
Frequently asked questions
How much does a W21x122 beam weigh?
W21x122 weighs 122 pounds per foot (181.6 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 2,440 lb and a 40 ft bar 4,880 lb.
What are the dimensions of a W21x122?
W21x122 is 21.7 in (551.2 mm) deep with a 12.4 in (315 mm) wide flange. The web is 0.6 in thick and the flanges are 0.96 in thick. Note the actual depth differs from the nominal W21 label — always design with the actual value.
What are the dimensions of a W21x122 in mm?
W21x122 is 551.2 mm deep with a 315 mm wide flange; the web is 15.2 mm and the flange 24.4 mm thick. In metric section properties: Ix = 123,204 cm⁴, Sx = 4,474 cm³.
How much does a W21x122 weigh in kg?
181.6 kg per meter. A 6 m bar weighs 1,089 kg and a 12 m bar 2,179 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W21x122?
About the strong axis, Ix = 2,960 in⁴ (123,204 cm⁴) with section modulus Sx = 273 in³. About the weak axis, Iy = 305 in⁴ and Sy = 49.2 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W21x122 or W21x132 — what does one size up change?
W21x132 is about 8% heavier (132 vs 122 lb/ft) but about 9% stiffer (Ix 3,220 vs 2,960 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