This is not well researched and should not be relied upon. But to get some idea of the relative size of steel and a glu lam I googled "beam for a 20 foot span". I don't know what they assumed for loading which can make a big difference. One item said 40 lbs/square foot. But with that caveat I got results indicating a W10x26 steel beam which is 5.75 in x 10 3/8 in or a W8x28 which is 6.5x8 inches would work. Or a glue laminated beam 3 1/8x19 or a beam 5 1/8x15 inches. Obviously the wood beam is much taller because wood does not resist deflection as well. Home floors are designed to keep deflection to the desired maximum under maximum loading, they are not designed to stay a certain percentage away from failure. 40 pounds per square foot is the normal assumption for the main living area in a house. If there are major loads (like a piano) that should probably be addressed. A hot tub would certainly need to be addressed. The 40 lbs per square foot is for just normal furniture and people.
To get reliable information you would want to look for information from a glu lam or steel beam provider. I have looked up glu lams before and found tables without a lot of digging. If you could hide the steel beam in a wall and let the joists rest on top of it the task for the carpenters would be a lot less than if they have to attach the ends of the joists to the beam.
The engineering design data available for engineered wood products is extensive. In most cases, in residential design, you can use tables to determine the spans of simple beams. You are dealing with dead loads, which are the loads that a beam will support, depending on a given dead load, and the live load that you design to. The values include deflection too, which are often determined by building code requirements. Of course, you can design a beam to exceed code requirements. However, tables are often inadequate when accounting for point loads on a beam.
The use of engineering software to design beams and other structural components allow not only the ability to apply loads to a beam that are not uniformly distributed - point loads - but the software provides an analysis of the loads applied to a structural member, that is presented in a graphic with the associated load values. The software can make recommendation of what structural members will work for the given design load specifications, giving you a choice of structural options.
When used correctly, you can graphically watch the impact of loads as they are carried down from the highest point in the structure, across various beams and girders, to vertical structural members, all the way to the footing. But you have to know how to use the software correctly, or there can be problems - big problems.
Over twenty-years-ago, I was building a three-story home and a local supplier was calculating the engineered wood components in the home. When I received the bid, I knew that something was very wrong. Using very sophisticated software, they had calculated the structural components for each level of the home in isolation. They had not added the loads of the previous levels to the lower levels. At multiple point loads, my software returned loads that could have easily resulted in a failure of the component. At the very least, the deflections would have been visibly noticeable, under dead load values alone.
Their software was as capable as mine, but someone at the building supply had unknowingly configured the software to isolate loads to each level, instead of transferring the loads of the upper levels downward. Merely checking the wrong box in the configuration menu put every home that they worked on at risk of structural problems, or worse.