Traditionally, conductors of choirs will not conduct using a baton unless they are leading a full orchestra along with their choir, whereas conductors of orchestras and other large ensembles will use a baton.
Using a baton is an additional skill; in programs of conducting pedagogy I've seen, all students will work with a baton in their first few semesters "...
There aren't any specific rules, conductors don't need to use a baton or in fact anything, but it makes it easier for the orchestra to see the conductor's movements.
Especially for those musicians further back, it just gives a nice specific timing point.
Since there's currently no answer here, I thought I'd do some digging. I haven't been able to get an exact number, but we can at least have a little fun getting an approximation.
In Boult's obituary in the New York Times, Edward Rothstein highlights Boult's
a baton that was nearly the length of his arm.
And in an activity created ...
I don't know if this topic is still active, but I thought I would reply to the excellent explanation by NReilingh from 2013.
I had the great honor and opportunity to sing under Dr Ernest G. Sullivan, PhD, at Alma College during the 1970's. We performed as an a cappella chorus of about 60 voices and in a madrigal group of 10-12 voices. Dr. Sullivan, who was ...