My well is making 50 gallons of water per minute How do I convert 50 gpm to PSI?

gpm and psi are two different measures that are not directly related, though a change in one will affect the other. To get the pressure at a certain point in your piping, you would need to measure it. Or, if you know that your pump is rated for 50 gpm at 80psi (1 foot water column = 2.31 psi) and your pump is lifting a column of water 15' (34.65 psi), then you should have about 45 psi residual. If you have long runs of horizontal pipe you may need to add some for pipe friction also.