W12x120 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W12x120 is an American wide-flange beam 13.1 inches (332.7 mm) deep with a 12.3 in (312.4 mm) flange, weighing 120 pounds per foot (178.6 kg/m) — that is what the "120" 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 | 13.1 in (332.7 mm) |
| Flange width bf | 12.3 in (312.4 mm) |
| Web thickness tw | 0.71 in (18 mm) |
| Flange thickness tf | 1.11 in (28.2 mm) |
Weight & Cross-Section
| Weight per foot | 120 lb/ft (178.6 kg/m) |
| 20 ft bar | 2,400 lb |
| 40 ft bar | 4,800 lb |
| Area A | 35.2 in² (227.1 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 1,070 in⁴ (44,537 cm⁴) |
| Section modulus Sx | 163 in³ (2,671 cm³) |
| Radius of gyration rx | 5.51 in |
| Moment of inertia Iy | 345 in⁴ (14,360 cm⁴) |
| Section modulus Sy | 56 in³ (918 cm³) |
| Radius of gyration ry | 3.13 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W12x106 | 12.9 × 12.2 | 106 | 933 | 145 | −12 % | −13 % |
| W12x120 (this page) | 13.1 × 12.3 | 120 | 1,070 | 163 | — | — |
| W12x136 | 13.4 × 12.4 | 136 | 1,240 | 186 | +13 % | +16 % |
Deflection example
A simply supported W12x120 spanning 21 ft with a 10 kip point load at midspan deflects 0.11 in (E = 29,000 ksi, Ix = 1,070 in⁴). The L/360 serviceability limit for this span is 0.7 in — the shape passes this quick check.
Calculate with your own span and load →
Frequently asked questions
How much does a W12x120 beam weigh?
W12x120 weighs 120 pounds per foot (178.6 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 2,400 lb and a 40 ft bar 4,800 lb.
What are the dimensions of a W12x120?
W12x120 is 13.1 in (332.7 mm) deep with a 12.3 in (312.4 mm) wide flange. The web is 0.71 in thick and the flanges are 1.11 in thick. Note the actual depth differs from the nominal W12 label — always design with the actual value.
What are the dimensions of a W12x120 in mm?
W12x120 is 332.7 mm deep with a 312.4 mm wide flange; the web is 18 mm and the flange 28.2 mm thick. In metric section properties: Ix = 44,537 cm⁴, Sx = 2,671 cm³.
How much does a W12x120 weigh in kg?
178.6 kg per meter. A 6 m bar weighs 1,072 kg and a 12 m bar 2,143 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W12x120?
About the strong axis, Ix = 1,070 in⁴ (44,537 cm⁴) with section modulus Sx = 163 in³. About the weak axis, Iy = 345 in⁴ and Sy = 56 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W12x120 or W12x136 — what does one size up change?
W12x136 is about 13% heavier (136 vs 120 lb/ft) but about 16% stiffer (Ix 1,240 vs 1,070 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