Measure the distance in inches that you need the steel beam to fill. Write this figure down on a sheet of paper as your clear span for the beam. Measure the length in inches of the floor joist that the I-beam must support. Divide that number by two.Click to see full answer. In this manner, how far can you span a steel beam?Yes. You can get a tall enough steel I-beam that will span 25 feet with no columns.Similarly, how do I choose steel beams? How to Select the I-Beam Specify the loading details of the steel I-beam. Draw the diagram for the bending moment based on the given details. Choose the estimated size of the steel I-beam. Find out the area moment of inertia of the steel I-beam. Find out the beam depth. Secondly, how do I know what size beam I need? The formula for the section modulus is beam width times beam depth squared divided by 6. A two 2-by-6 standard beam has actual dimensions of 1.5-by-5.5 inches which would give a section modulus of 1.5 x 5.5 x 5.5 / 6 = 7.6 which is not enough for this example. A 2-by-8 beam would be sufficient.How far can a beam span without support?When supporting joists that span 12 feet with no overhang beyond the beam, a double ply beam can span in feet a value equal to its depth in inches. A double 2×12 beam can span 12 feet; a (2) 2×10 can span 10 feet and so on.