W8x13 — Dimensions, Weight & Section Properties
American wide-flange (W) beam per ASTM A6 / AISC Steel Construction Manual
W8x13 is an American wide-flange beam 7.99 inches (202.9 mm) deep with a 4 in (101.6 mm) flange, weighing 13 pounds per foot (19.3 kg/m) — that is what the "13" 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 | 7.99 in (202.9 mm) |
| Flange width bf | 4 in (101.6 mm) |
| Web thickness tw | 0.23 in (5.8 mm) |
| Flange thickness tf | 0.255 in (6.5 mm) |
Weight & Cross-Section
| Weight per foot | 13 lb/ft (19.3 kg/m) |
| 20 ft bar | 260 lb |
| 40 ft bar | 520 lb |
| Area A | 3.84 in² (24.8 cm²) |
Section Properties (strong / weak axis)
| Moment of inertia Ix | 39.6 in⁴ (1,648 cm⁴) |
| Section modulus Sx | 9.91 in³ (162 cm³) |
| Radius of gyration rx | 3.21 in |
| Moment of inertia Iy | 2.73 in⁴ (114 cm⁴) |
| Section modulus Sy | 1.37 in³ (22 cm³) |
| Radius of gyration ry | 0.84 in |
Compared with the neighbouring sizes
| Shape | d × bf (in) | lb/ft | Ix (in⁴) | Sx (in³) | Δ weight | Δ Ix |
|---|---|---|---|---|---|---|
| W8x10 | 7.89 × 3.94 | 10 | 30.8 | 7.81 | −23 % | −22 % |
| W8x13 (this page) | 7.99 × 4 | 13 | 39.6 | 9.91 | — | — |
| W8x15 | 8.11 × 4.02 | 15 | 48 | 11.8 | +15 % | +21 % |
Deflection example
A simply supported W8x13 spanning 13 ft with a 10 kip point load at midspan deflects 0.69 in (E = 29,000 ksi, Ix = 39.6 in⁴). The L/360 serviceability limit for this span is 0.43 in — the shape does NOT pass this quick check.
Calculate with your own span and load →
Frequently asked questions
How much does a W8x13 beam weigh?
W8x13 weighs 13 pounds per foot (19.3 kg/m). The number after the "x" in the designation is always the weight in lb/ft. A 20 ft bar weighs 260 lb and a 40 ft bar 520 lb.
What are the dimensions of a W8x13?
W8x13 is 7.99 in (202.9 mm) deep with a 4 in (101.6 mm) wide flange. The web is 0.23 in thick and the flanges are 0.26 in thick. Note the actual depth differs from the nominal W8 label — always design with the actual value.
What are the dimensions of a W8x13 in mm?
W8x13 is 202.9 mm deep with a 101.6 mm wide flange; the web is 5.8 mm and the flange 6.5 mm thick. In metric section properties: Ix = 1,648 cm⁴, Sx = 162 cm³.
How much does a W8x13 weigh in kg?
19.3 kg per meter. A 6 m bar weighs 116 kg and a 12 m bar 232 kg — handy when ordering US shapes from metric suppliers.
What is the moment of inertia of a W8x13?
About the strong axis, Ix = 39.6 in⁴ (1,648 cm⁴) with section modulus Sx = 9.91 in³. About the weak axis, Iy = 2.73 in⁴ and Sy = 1.37 in³. Use the beam deflection calculator to turn these into deflection and stress for your span and load.
W8x13 or W8x15 — what does one size up change?
W8x15 is about 15% heavier (15 vs 13 lb/ft) but about 21% stiffer (Ix 48 vs 39.6 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