You are the second person I have come across that uses PI to get software estimates. "I am not sure why but it works, except when it doesnt then I know exactly why"

What I found was most people over/under estimate things. They also tend to do it consistently at the same rate. Typically they have a scaling factor you can use. Around 3 seems to be the sweet spot for most people. You could just as easily use 3.1 or 3.2 and get a similar answer. I usually go for 3 because I can do that in my head without a calculator.