W12x40 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W12x40 is an American wide-flange beam 11.9 inches (302.3 mm) deep with a 8.01 in (203.5 mm) flange, weighing 40 pounds per foot (59.5 kg/m) — that is what the "40" 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 | 11.9 in (302.3 mm) |
| Flange width bf | 8.01 in (203.5 mm) |
| Web thickness tw | 0.295 in (7.5 mm) |
| Flange thickness tf | 0.515 in (13.1 mm) |
Weight & Cross-Section
| Weight per foot | 40 lb/ft (59.5 kg/m) |
| 20 ft bar | 800 lb |
| 40 ft bar | 1,600 lb |
| Area A | 11.7 in² (75.5 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 307 in⁴ (12,778 cm⁴) |
| Section modulus Sx | 51.5 in³ (844 cm³) |
| Radius of gyration rx | 5.13 in |
| Moment of inertia Iy | 44.1 in⁴ (1,836 cm⁴) |
| Section modulus Sy | 11 in³ (180 cm³) |
| Radius of gyration ry | 1.94 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W12x35 | 12.5 × 6.56 | 35 | 285 | 45.6 | −12 % | −7 % |
| W12x40 (this page) | 11.9 × 8.01 | 40 | 307 | 51.5 | — | — |
| W12x45 | 12.1 × 8.05 | 45 | 348 | 57.7 | +13 % | +13 % |
Deflection example
A simply supported W12x40 spanning 19 ft with a 10 kip point load at midspan deflects 0.28 in (E = 29,000 ksi, Ix = 307 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 W12x40 beam weigh?
W12x40 weighs 40 pounds per foot (59.5 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 800 lb and a 40 ft bar 1,600 lb.
What are the dimensions of a W12x40?
W12x40 is 11.9 in (302.3 mm) deep with a 8.01 in (203.5 mm) wide flange. The web is 0.3 in thick and the flanges are 0.52 in thick. Note the actual depth differs from the nominal W12 label — always design with the actual value.
What are the dimensions of a W12x40 in mm?
W12x40 is 302.3 mm deep with a 203.5 mm wide flange; the web is 7.5 mm and the flange 13.1 mm thick. In metric section properties: Ix = 12,778 cm⁴, Sx = 844 cm³.
How much does a W12x40 weigh in kg?
59.5 kg per meter. A 6 m bar weighs 357 kg and a 12 m bar 714 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W12x40?
About the strong axis, Ix = 307 in⁴ (12,778 cm⁴) with section modulus Sx = 51.5 in³. About the weak axis, Iy = 44.1 in⁴ and Sy = 11 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W12x40 or W12x45 — what does one size up change?
W12x45 is about 13% heavier (45 vs 40 lb/ft) but about 13% stiffer (Ix 348 vs 307 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