Area irrigated by a pump
What is the maximum possible irrigated area from a specific horsepower pump? Will a pump of a certain horsepower supply the irrigation area you need? This is a simple calculation because horsepower divided by water head (pressure) equals flow. And flow multiplied by irrigation time, and divided by depth of water to replace evapotranspiration, is irrigation area.
You will need to know the worst case evapotranspiration per week, e.g., 1.3 inches per week (assumes it does not rain).
You will need to know how many hours per week you can irrigate. For example, is there a local water restriction allowing irrigation only certain hours and days? Do users prefer there be no irrigation on certain days and hours?
You will need to know or guess the pump efficiency and the pressure at the pump. Both of which you can get from the pump curve. There is a small tweak for lift.
Irrigation system limitations
The converter does not account for friction loss in pipes which will reduce total system efficiency. (Which is different from pump efficiency.) The converter assumes irrigation zones can efficiently utilize maximum pumping capacity, if need be, by running zones simultaneously.