A 6 inch deep steel section can substitute for a wooden girder 14 inches deep, thus saving headroom.
The following table gives the allowable loads for steel beams and it indicates two different types of cross sections. The most popular I-beam is designated on the table as an "S" section, as shown in Figure 1. The "S" stands for slim. The "W" designation refers to a steel section with wider flanges, as shown in Figure 2, than the "S" section.
Figure 1 - "S" style I-beam
Figure 2 - "W" style I-beam
Safe Loads In Pounds For Steel I-Beams & Girders