Rate, velocity and why the bore decides both
A flow rate answers a different question from a pipe volume. Volume asks what is sitting in the line right now. Rate asks how much goes past a point every minute while the tap is open. You need the rate to say whether a run can feed what hangs off it, to size a pump, or to work out how long a fill takes.
One relationship does all of it: the flow equals the cross-sectional area of the bore multiplied by how fast the water is traveling. That makes the inner diameter the input that carries the answer, and it carries it as a square. Go from a 20 mm bore to a 25 mm bore at the same velocity and you move about 56 percent more water. Take the inside measurement: a nominal size on the label is a name, not a dimension, and it is rarely what the pipe carries.
Read the rate and the velocity together. The rate tells you whether there is enough water. The velocity tells you what the run will be like to live with: noise through a wall, and wear on the inside of every elbow. The figure for the top of that range belongs to the design, the pipe maker or the code official, so this tool asks you for it rather than inventing one.
The common mistake is reading a rate as a quantity. Sixty liters a minute is not sixty liters; it is sixty liters for every minute it runs, which is why the duration field is there. Zeus lets you photograph the meter and the nameplate and keep them on the job, so the figures behind a number like this are still there when somebody questions it.
ZEUS