When most people say "I-beam" they mean one of two things: the older American Standard I-beam (S-shape) with relatively narrow flanges, or the modern wide-flange section (W-shape) that has largely replaced it. These are distinct shapes with different proportions, different section properties, and different connection details. This guide covers both.
S-Shape vs W-Shape
S-shape (American Standard I-beam): Relatively narrow flanges (approximately 50–60% of section depth) with a noticeable inner flange taper (~9.5°). The taper suits crane runway beams where crane hooks engage the bottom flange. Designation: S[nominal depth] × [weight per foot].
W-shape (Wide Flange): Nearly parallel flanges (very small taper, typically 1:20 or ~2.9°), with flange width often approaching or equaling section depth. More material in the flanges relative to the web maximizes moment of inertia per unit weight. The standard structural beam in North American construction. Designation: W[nominal depth] × [weight per foot].
Nominal Depth vs Actual Depth
The "W12" in "W12 × 26" is a nominal depth label, not the actual section depth. Within a given nominal depth group, the rolling mill uses a single base pass that defines the outer profile. Heavier sections within the group are achieved by varying pass thickness, which slightly changes the actual depth.
W12 × 26: actual depth = 12.22" (not 12.00")W18 × 35: actual depth = 17.70" (not 18.00")W18 × 97: actual depth = 18.59"
For structural calculations, always use actual depth from the AISC Manual. For connection plates, note that a "W18 beam" varies in actual depth by nearly 1" depending on weight — always specify the full designation.
W-Shape Dimensions
All from AISC Steel Construction Manual. d = actual depth, bf = flange width, tf = flange thickness, tw = web thickness, Ix = strong-axis moment of inertia.
W4 through W8
| Designation | d (in) | bf (in) | tf (in) | tw (in) | Ix (in⁴) | Weight (lb/ft) |
|---|---|---|---|---|---|---|
| W4 × 13 | 4.16 | 4.060 | 0.345 | 0.280 | 11.3 | 13 |
| W6 × 9 | 5.90 | 3.940 | 0.215 | 0.170 | 16.4 | 9 |
| W6 × 15 | 5.99 | 5.990 | 0.260 | 0.230 | 29.1 | 15 |
| W6 × 20 | 6.20 | 6.020 | 0.365 | 0.260 | 41.4 | 20 |
| W6 × 25 | 6.38 | 6.080 | 0.455 | 0.320 | 53.4 | 25 |
| W8 × 10 | 7.89 | 3.940 | 0.205 | 0.170 | 30.8 | 10 |
| W8 × 18 | 8.14 | 5.250 | 0.330 | 0.230 | 61.9 | 18 |
| W8 × 31 | 8.00 | 7.995 | 0.435 | 0.285 | 110 | 31 |
| W8 × 40 | 8.25 | 8.070 | 0.560 | 0.360 | 146 | 40 |
| W8 × 48 | 8.50 | 8.110 | 0.685 | 0.400 | 184 | 48 |
W10 through W12
| Designation | d (in) | bf (in) | tf (in) | tw (in) | Ix (in⁴) | Weight (lb/ft) |
|---|---|---|---|---|---|---|
| W10 × 12 | 9.87 | 3.960 | 0.210 | 0.190 | 53.8 | 12 |
| W10 × 22 | 10.17 | 5.750 | 0.360 | 0.240 | 118 | 22 |
| W10 × 33 | 9.73 | 7.960 | 0.435 | 0.290 | 170 | 33 |
| W10 × 45 | 10.10 | 8.020 | 0.620 | 0.350 | 248 | 45 |
| W10 × 60 | 10.22 | 10.080 | 0.680 | 0.420 | 341 | 60 |
| W12 × 14 | 11.91 | 3.970 | 0.225 | 0.200 | 88.6 | 14 |
| W12 × 26 | 12.22 | 6.490 | 0.380 | 0.230 | 204 | 26 |
| W12 × 40 | 11.94 | 8.005 | 0.515 | 0.295 | 307 | 40 |
| W12 × 65 | 12.12 | 12.000 | 0.605 | 0.390 | 533 | 65 |
W14 through W18
| Designation | d (in) | bf (in) | tf (in) | tw (in) | Ix (in⁴) | Weight (lb/ft) |
|---|---|---|---|---|---|---|
| W14 × 22 | 13.74 | 5.000 | 0.335 | 0.230 | 199 | 22 |
| W14 × 30 | 13.84 | 6.730 | 0.385 | 0.270 | 291 | 30 |
| W14 × 43 | 13.66 | 7.995 | 0.530 | 0.305 | 428 | 43 |
| W14 × 53 | 13.92 | 8.060 | 0.660 | 0.370 | 541 | 53 |
| W16 × 26 | 15.69 | 5.500 | 0.345 | 0.250 | 301 | 26 |
| W16 × 36 | 15.86 | 6.985 | 0.430 | 0.295 | 448 | 36 |
| W16 × 50 | 16.26 | 7.073 | 0.630 | 0.380 | 659 | 50 |
| W18 × 35 | 17.70 | 6.000 | 0.425 | 0.300 | 510 | 35 |
| W18 × 50 | 17.99 | 7.495 | 0.570 | 0.355 | 800 | 50 |
| W18 × 76 | 18.21 | 11.035 | 0.680 | 0.425 | 1330 | 76 |
W21 through W24
| Designation | d (in) | bf (in) | tf (in) | tw (in) | Ix (in⁴) | Weight (lb/ft) |
|---|---|---|---|---|---|---|
| W21 × 44 | 20.66 | 6.500 | 0.530 | 0.350 | 843 | 44 |
| W21 × 62 | 20.99 | 8.240 | 0.615 | 0.400 | 1330 | 62 |
| W24 × 55 | 23.57 | 7.005 | 0.505 | 0.395 | 1350 | 55 |
| W24 × 76 | 23.92 | 8.990 | 0.680 | 0.440 | 2100 | 76 |
S-Shape (American Standard I-Beam) Reference
| Designation | d (in) | bf (in) | tf (in) | tw (in) | Ix (in⁴) | Weight (lb/ft) |
|---|---|---|---|---|---|---|
| S3 × 5.7 | 3.00 | 2.330 | 0.359 | 0.170 | 2.52 | 5.7 |
| S5 × 10.0 | 5.00 | 3.004 | 0.326 | 0.214 | 12.3 | 10.0 |
| S8 × 18.4 | 8.00 | 4.001 | 0.426 | 0.271 | 57.6 | 18.4 |
| S8 × 23.0 | 8.00 | 4.171 | 0.426 | 0.441 | 64.9 | 23.0 |
| S10 × 25.4 | 10.00 | 4.661 | 0.491 | 0.311 | 124 | 25.4 |
| S12 × 31.8 | 12.00 | 5.000 | 0.544 | 0.350 | 218 | 31.8 |
Column vs Beam Selection
W-shapes serve as both beams and columns, but different shape families are optimized for each role.
Beam-optimized (bending): Deep sections with narrow flanges maximize Ix about the strong axis. W16, W18, W21, W24, and deeper sections. Low bf/d ratio (flange much narrower than depth).
Column-optimized (compression + biaxial bending): Compact sections where flange width approaches depth. W6, W8, W10, W12 sections with wide flanges (bf/d close to 1.0). These resist bending in both axes efficiently.
| Shape | d (in) | bf (in) | bf/d | Best Use |
|---|---|---|---|---|
| W6 × 25 | 6.38 | 6.08 | 0.95 | Column |
| W8 × 31 | 8.00 | 7.995 | 1.00 | Column |
| W12 × 65 | 12.12 | 12.00 | 0.99 | Column |
| W18 × 35 | 17.70 | 6.00 | 0.34 | Beam |
| W24 × 76 | 23.92 | 8.99 | 0.38 | Beam |
Related Shape Families
HP-shapes (bearing piles): Look like W-shapes but with equal flange and web thickness — designed to withstand end-bearing pile driving forces. Example: HP12 × 53.
M-shapes (miscellaneous): Small shapes that don't fit W or S rolling schedules. Rarely used in new design.
Built-up sections: Fabricated by welding plate into I or box shapes when no standard section provides the required section modulus, depth, or flange width.
Connection Plate Basics
Shear tabs and end plates: The most common field-bolted connections. A shear tab is a plate welded to the column face with bolt holes matching the beam web.
Coping: When a W-shape beam frames into another beam at the same depth, the top flange must be coped (cut back) to clear the supporting flange. Cope depth = flange thickness + 1/4" clearance.
Cope reduces capacity: Removing the flange significantly reduces shear capacity. AISC requires a local buckling check for coped beams. For heavily loaded beams with long copes, a reinforcing plate may be required.
Column base plates: Welded or placed under a W-shape column to distribute load to the footing. Size and anchor bolt pattern per AISC Design Guide 1. Base plate must project beyond column flanges on all sides.