If L, D and f are the length, diameter and coefficient of friction of a pipe, the ratio of the areas of the pipe A and nozzle a, to transmit maximum power, is

If the length of the pipe is doubled, the head loss will double. If the inside pipe diameter is doubled, the head loss will be reduced by half. If the flow rate is doubled, the head loss increases by a factor of four. With the exception of the Darcy friction factor, each of these terms can be easily measured.