You would never use a calculator or guessing to come up with gearing when drag racing. Track time, trial and error to get the best 60 foot times are the only way. No amount of calculating will do this.
On my big turbo Kawasaki's, the best 60's are reached with gearing so high that would only have us using 4 of the 5 gears. In drag racing you first focus on 60 foot times, once they are optimized everything will fall into place.