"Crawl ratios" and calculating same

[PB Schechter <pb@domain.elided>]

All this talk about "crawl ratios" has me wondering how to calculate them.
I have a '65 T'all, with what the line setting ticket calls the T-16 (it is
a 4-speed, with a 6.8:1 (or close) 1st gear) transmission, a transfer case
that I don't remember, and 4.09 differentials.  So, do I just multiply the
ratios to calculate a final ratio?  Is there a table I need to use?  There
must be some effect of tire size on all of this.  Can anyone post a (brief)
tutorial, or point me to where I can find the answer?

Thanks in avance.

PB Schechter
pb@domain.elided