I'm looking to replace a 2x6 wall 16" on center 25' spread with a steel i beam 12' tall. Looking for a calcolation in size and weight

A steel beam 12 feet tall? You mean 12 inches, I presume.

Determining the beam to use depends on specifying the load it must carry, which in this case means how many floors are above and what their use are (i.e. living space versus attic), and/or the roof. Also, while we can do a calculation on this, you must have an engineer detail and sign off on the plan for your building permit.