*just under 5 gpm, I mean!

They are 2 different measurements, one is pressure, one is flow. Flow can vary depending on pressure, so there really isn't a way to do this. If you want to know your pressure, get a pressure gauge. If you want to measure your flow gpm. Fill a 5 gallon bucked for 15 seconds, measure it, multiply by 4, then divide by 60. Hope this helps some.

Thanks Goldie. I saw psi to gpm conversions so I couldn't figure out what the problem was.
I will buy a pressure gauge!