LTSpice: When running a linear AC simulation, how to view the voltage ratio between two voltages?
As you can read here, LTSpice can plot a mathematical function of the traced variables.  You just have to edit the plot to specify the functions.

An example from the from the linked page is shown below.  As mentioned in the comments, to edit the plot function you can right click on the name.  The plot name is the green string starting with "1.1*pow...".