Steel Beam Weight: W-Shape, S-Shape, and Structural Steel Sizing Explained
Reviewed by Jerry Croteau, Founder & Editor
Table of Contents
Steel beams are specified by a designation system that tells you the shape, nominal depth, and weight per foot in a single label. A W12x26 is a wide-flange beam, 12 inches nominally deep, weighing 26 pounds per linear foot. Once you understand the system, calculating total weight for any span is straightforward.
Our handles bar stock, plate, and structural sections. This guide covers structural shapes and how to use them for load planning and procurement.
The three primary structural shapes
W-shape (Wide Flange)
The most common structural shape in North American construction. Parallel flanges make W-shapes more efficient for bending than older I-beam designs. The designation W[depth]x[weight/ft].
- W6x9 — 6" deep, 9 lbs/ft (smallest common W-shape)
- W8x31 — 8" deep, 31 lbs/ft
- W12x26 — 12" deep, 26 lbs/ft (very common in residential/light commercial)
- W14x48 — 14" deep, 48 lbs/ft
- W24x94 — 24" deep, 94 lbs/ft (heavy commercial/industrial)
Note: the nominal depth is approximate. A W12x26 has an actual depth of 12.22 inches. Actual dimensions are in the AISC Steel Construction Manual.
S-shape (Standard I-Beam)
Older designation with sloped inner flange faces. Less efficient than W-shapes for most modern applications but still common in older structures and some specific uses. Designation S[depth]x[weight/ft].
C-shape (Channel)
C-shaped cross section, used for purlins, girts, and secondary framing. Designation C[depth]x[weight/ft]. For example, C6x13 is 6 inches deep, 13 lbs/ft.
Common W-shape weights per foot
| Designation | Depth (actual) | Flange width | Weight (lbs/ft) |
|---|---|---|---|
| W6x9 | 5.90" | 3.94" | 9 |
| W8x18 | 8.14" | 5.25" | 18 |
| W10x22 | 10.17" | 5.75" | 22 |
| W12x26 | 12.22" | 6.49" | 26 |
| W12x40 | 11.94" | 8.01" | 40 |
| W14x48 | 13.79" | 8.031" | 48 |
| W16x57 | 16.43" | 7.12" | 57 |
| W18x65 | 18.35" | 7.59" | 65 |
| W21x68 | 21.13" | 8.27" | 68 |
| W24x84 | 24.10" | 9.02" | 84 |
Calculating total beam weight
Total weight = Weight per foot x Length (feet)
Examples
A W12x26 spanning 22 feet:
Total = 26 x 22 = 572 lbs
Four W14x48 beams each spanning 30 feet:
Total = 4 x (48 x 30) = 4 x 1,440 = 5,760 lbs
A structural package for a steel building frame:
- 8 columns: W8x31, 14 ft each = 8 x (31 x 14) = 3,472 lbs
- 4 girders: W14x48, 30 ft each = 4 x (48 x 30) = 5,760 lbs
- 12 beams: W12x26, 15 ft each = 12 x (26 x 15) = 4,680 lbs
- Total structural steel = 13,912 lbs (~7 tons)
What affects beam selection
Structural engineers size beams based on three primary criteria:
- Bending moment capacity: The beam must resist the maximum bending stress from applied loads. Deeper beams and heavier sections have higher moment capacity.
- Shear capacity: The web of the beam must handle vertical shear forces near supports.
- Deflection limits: Most codes limit live load deflection to L/360 (span in inches / 360). A 20-foot beam (240 inches) should not deflect more than 240/360 = 0.67 inches under live load.
For a given span and load, the lightest beam that meets all three criteria is typically the most economical choice. This is why beam tables in the AISC manual list section properties — engineers compare moment of inertia (I), section modulus (S), and plastic section modulus (Z) rather than just depth or weight.
Steel density and custom section weights
All structural steel is carbon steel with a density of approximately 490 lbs/ft³ (7,850 kg/m³). For non-standard shapes or custom fabrications:
Weight per foot = Cross-sectional area (in²) x 3.4 lbs/in²/ft
A flat bar 6 inches wide, 1/2 inch thick:
Area = 6 x 0.5 = 3 in²
Weight/ft = 3 x 3.4 = 10.2 lbs/ft
This factor (3.4) comes from converting the density: 490 lbs/ft³ x (1 ft³ / 1,728 in³) = 0.2836 lbs/in³, times 12 inches = 3.403 lbs per inch of cross-sectional area per foot of length.
Procurement and mill ordering
Structural steel is available in standard mill lengths (typically 20, 30, 40, or 60 feet) or cut-to-length. Steel service centers stock the most common sections. Ordering strategies:
- Always add 2-3% to calculated quantities for waste and cutting losses
- Standard mill lengths reduce cutting waste; design spans to use standard lengths when possible
- Galvanized structural steel adds 3-5% to base weight
- Primer coat adds negligible weight
Calculate total weight for any structural steel package using the or the which covers bars, plates, tubes, and pipes alongside structural shapes.
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