It depends on the amount of work you want the pump to do. If you want to use it over a large area like, a huge yard, you will need quite a powerful sprinkler pump. If you are dealing with, say, ten spray heads with a rating of 4gpm, you’ll need a pump that can pump at the same or higher rate.You can determine the field size your pump will be working on and multiply by the amount of water in inches it will require. Converting to gallons will enable you to know the size and power of the pump you need.