All pumps, powerheads have a gph rating. If you do not know what it is, look up your style/model on any website that sells your product and that will tell you your gph. You might have to do a liitle searching.
Yeah I know the rating but when you have distance and 90 degree elbows and Up flow that all takes away from the GPH.
That is why I wanted to know how to interpret the calculator.