SCOTUS Judges tend to stay a while

Did some really simple number-crunching after I heard John Roberts would be the 109th Supreme Court judge. Wow, I thought- there have been only 109 Supreme Court judges while there have been 45 presidents to date. Since there are nine SC judges, that indicates the judges tend to serve far longer than the average president. I realize that's a pretty well known fact but I crunched the numbers anyway.

Facts - there are nine SCOTUS judges and I think that has been the case since 1776. There is only one president (not counting the co-prez Hillary) at a time. So I divided the 109 total judges by 9 to get me the quasi "full-time equivalent" to a single president. [ 109 / 9 = 12.1]

Next I divided the 45 presidents by the 12.1 FTE judges. That gives the term or length of service equivalency for the average SCOTUS judge vs. the average president. [ 45 / 12.1 = 3.71] . In other words, the average SCOTUS judge serves 3.71 times as long as the average president. Since 1776, we have had 45 presidents who served an average of 5.1 years.

Bottom line is the average SCOTUS judge serves 18.9 years vs. the average president who serves 5.1 years [calculation was 5.1 years for president X 3.71 = 18.9 average years for a judge]. To me, this is an eye-opening stat and certainly speaks to the potentially significant impact of a SCOTUS appointment. Especially in these supposedly litigous times! On the other hand, it somewhat defuses the DEMS complaint that Roberts will likely serve a very long time. If the average has been 18.9 years, Roberts will not reach that until he is almost 70 years old and once you reach that age, anything can happen.