so....how d o you calculate your ballpark top tube length?

I was using the formula in Zinn's book...but the numbers came out so freakin wacky!!

look:
My arm is 22"
my torso minus "crotch" height is 30.2 + 22 = 52.2 multiply by 0.467 *(?) is 24.3"

24.3" = 61.7 cm ?????? for a top tube. Nonew of the geometrys I looked at had numbers anywhere near that.


*i'm at workand don't have the book