It would be convenient for the cognoscenti of law department management to be able to describe numerically levels and spans of control. For example, if a 10lawyer department has four lawyers who report to the general counsel (“direct reports”), the general counsel’s supervisory ratio is 4:1. The remaining five lawyers of the level below the direct reports (“secondlevel reports”) would give the direct reports a ratio of 1.25:1 (5 lawyers divided by 4), if none of the secondlevel lawyers has a lawyer report.
Likewise, if a 20lawyer department has six direct reports to the general counsel, that general counsel has a 6:1 supervisory ratio. The remaining 13 lawyers means that the second level reports, assuming no levels below the third level of lawyers, have a ratio of 2.2:1.
If we assume that the number of direct reports to a general counsel tops out at seven, then a law department with 100 lawyers would have 92 of them reporting ultimately to those seven directreport lawyers, an ultimate supervisory ratio of 13.1: 1.
Five further thoughts on the above calculations:

We need a supervisory ratio for each level. The more lawyers in a law department, the higher the supervisory metric goes unless you calculate it for each level down. The supervisory ratio shrinks as you move down through the organization, both because there are fewer lawyers at each more junior level and because supervisors have less managerial experience and therefore can handle only a few reports.

Some clever math should allow us to combine the ratios of each level into one figure. If we merely combine the reporting levels of the general counsel and his or her direct reports, the 10lawyer department has a ratio of 9 to 4, which is 2.2:1 (4 to 1 plus 5 to 4). But that makes little sense.

The wider the span of control of the general counsel, the smaller the direct reports’ ratio if we hold constant the size of departments.

The supervisory ratio should include paralegals and support staff if they report to lawyers, because everybody who is supervised requires some managerial attention. If we include all reports, the supervisory ratios approximately double because most law departments have about one nonlawyer for every lawyer.

Since each level down has less of a supervisory burden, you might reduce the supervisory ratio of each level down by a percentage, such as to subtract from one the result of one divided by the number of levels. Thus the fourth level of lawyers would have their supervisory ratio reduced by 75% (1 minus ¼).