The amount of GPM for is decided on by the motor size. By looking at the charts provided you can decide what amount of fluid you will need. There is range for each size that can be run, which we call running on the “low side” of that range or the “high side” of that range. The larger the motor the more distance in between low side and high side. Optimum range would be the ideal GPM for that motor. For instance a 3 1⁄2” 6-7 Lobe Drilling Motor range would be 60 to 70 GPM. 60 GMP would be the low side, 70 GPM would be the High Side & optimum would be in the middle.