W16x31 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W16x31 is an American wide-flange beam 15.9 inches (403.9 mm) deep with a 5.53 in (140.5 mm) flange, weighing 31 pounds per foot (46.1 kg/m) — that is what the "31" 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 | 15.9 in (403.9 mm) |
| Flange width bf | 5.53 in (140.5 mm) |
| Web thickness tw | 0.275 in (7 mm) |
| Flange thickness tf | 0.44 in (11.2 mm) |
Weight & Cross-Section
| Weight per foot | 31 lb/ft (46.1 kg/m) |
| 20 ft bar | 620 lb |
| 40 ft bar | 1,240 lb |
| Area A | 9.13 in² (58.9 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 375 in⁴ (15,609 cm⁴) |
| Section modulus Sx | 47.2 in³ (773 cm³) |
| Radius of gyration rx | 6.41 in |
| Moment of inertia Iy | 12.4 in⁴ (516 cm⁴) |
| Section modulus Sy | 4.49 in³ (74 cm³) |
| Radius of gyration ry | 1.17 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W16x26 | 15.7 × 5.5 | 26 | 301 | 38.4 | −16 % | −20 % |
| W16x31 (this page) | 15.9 × 5.53 | 31 | 375 | 47.2 | — | — |
| W16x36 | 15.9 × 6.99 | 36 | 448 | 56.5 | +16 % | +19 % |
Deflection example
A simply supported W16x31 spanning 25 ft with a 10 kip point load at midspan deflects 0.52 in (E = 29,000 ksi, Ix = 375 in⁴). The L/360 serviceability limit for this span is 0.83 in — the shape passes this quick check.
Calculate with your own span and load →
Frequently asked questions
How much does a W16x31 beam weigh?
W16x31 weighs 31 pounds per foot (46.1 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 620 lb and a 40 ft bar 1,240 lb.
What are the dimensions of a W16x31?
W16x31 is 15.9 in (403.9 mm) deep with a 5.53 in (140.5 mm) wide flange. The web is 0.28 in thick and the flanges are 0.44 in thick. Note the actual depth differs from the nominal W16 label — always design with the actual value.
What are the dimensions of a W16x31 in mm?
W16x31 is 403.9 mm deep with a 140.5 mm wide flange; the web is 7 mm and the flange 11.2 mm thick. In metric section properties: Ix = 15,609 cm⁴, Sx = 773 cm³.
How much does a W16x31 weigh in kg?
46.1 kg per meter. A 6 m bar weighs 277 kg and a 12 m bar 554 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W16x31?
About the strong axis, Ix = 375 in⁴ (15,609 cm⁴) with section modulus Sx = 47.2 in³. About the weak axis, Iy = 12.4 in⁴ and Sy = 4.49 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W16x31 or W16x36 — what does one size up change?
W16x36 is about 16% heavier (36 vs 31 lb/ft) but about 19% stiffer (Ix 448 vs 375 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