W12x45 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W12x45 is an American wide-flange beam 12.1 inches (307.3 mm) deep with a 8.05 in (204.5 mm) flange, weighing 45 pounds per foot (67 kg/m) — that is what the "45" 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 | 12.1 in (307.3 mm) |
| Flange width bf | 8.05 in (204.5 mm) |
| Web thickness tw | 0.335 in (8.5 mm) |
| Flange thickness tf | 0.575 in (14.6 mm) |
Weight & Cross-Section
| Weight per foot | 45 lb/ft (67 kg/m) |
| 20 ft bar | 900 lb |
| 40 ft bar | 1,800 lb |
| Area A | 13.1 in² (84.5 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 348 in⁴ (14,485 cm⁴) |
| Section modulus Sx | 57.7 in³ (946 cm³) |
| Radius of gyration rx | 5.15 in |
| Moment of inertia Iy | 50 in⁴ (2,081 cm⁴) |
| Section modulus Sy | 12.4 in³ (203 cm³) |
| Radius of gyration ry | 1.95 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W12x40 | 11.9 × 8.01 | 40 | 307 | 51.5 | −11 % | −12 % |
| W12x45 (this page) | 12.1 × 8.05 | 45 | 348 | 57.7 | — | — |
| W12x50 | 12.2 × 8.08 | 50 | 391 | 64.2 | +11 % | +12 % |
Deflection example
A simply supported W12x45 spanning 19 ft with a 10 kip point load at midspan deflects 0.25 in (E = 29,000 ksi, Ix = 348 in⁴). The L/360 serviceability limit for this span is 0.63 in — the shape passes this quick check.
Calculate with your own span and load →
Frequently asked questions
How much does a W12x45 beam weigh?
W12x45 weighs 45 pounds per foot (67 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 900 lb and a 40 ft bar 1,800 lb.
What are the dimensions of a W12x45?
W12x45 is 12.1 in (307.3 mm) deep with a 8.05 in (204.5 mm) wide flange. The web is 0.34 in thick and the flanges are 0.58 in thick. Note the actual depth differs from the nominal W12 label — always design with the actual value.
What are the dimensions of a W12x45 in mm?
W12x45 is 307.3 mm deep with a 204.5 mm wide flange; the web is 8.5 mm and the flange 14.6 mm thick. In metric section properties: Ix = 14,485 cm⁴, Sx = 946 cm³.
How much does a W12x45 weigh in kg?
67 kg per meter. A 6 m bar weighs 402 kg and a 12 m bar 804 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W12x45?
About the strong axis, Ix = 348 in⁴ (14,485 cm⁴) with section modulus Sx = 57.7 in³. About the weak axis, Iy = 50 in⁴ and Sy = 12.4 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W12x45 or W12x50 — what does one size up change?
W12x50 is about 11% heavier (50 vs 45 lb/ft) but about 12% stiffer (Ix 391 vs 348 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