Well diameter should be determined as per the pump size, it should not be the other way around
To size a well pump there are two main things which needs to be considered i.e. your required flow rate and your required amount of lift
Flow rate: it is the volume of fluid travelled in unit time (usually measured in LPM or GPM or m3/h) Lift: amount of lift can also be determined as total dynamic head (usually measured in mtr. Or ft.)
Determine TDH (Total Dynamic Head)
TDH = Pumping level + Vertical Lift + Friction loss (pipe and fittings)
Determine Friction losses
Friction losses = Total length of pipe*Friction loss factor + Friction loss of fittings
Completing this questionnaire will help us to understand your water pumping needs more accurately. Not all questions may apply to your situation but please give us as much information as you can.