Secondary voltage

I am curious as to the voltage potential being produced by my coil.  I have
seen this discussed before but I don't remember the details.  If my system is
producing 70" discharges, what is the approximate voltage?  I know it depends
on humidity and atmospheric pressure.  My house is about 2500 feet above sea
level.  Humidity here is usually low, probably 50% or less.  Is it something
like 40 or 50kv per inch?

Thanks,  Ed Sonderman