I figured he would be talking about domestic. However, there is no need to figure open flow that way. You need residual pressure at the end of the pipe to be of any use, so different design standards would apply.
The opposite approach should be taken. The pipe should be sized for the flow and pressure drop. The size should also limit the velocity to under 8 feet per second to be reasonable. 10 feet per second and more can cause errosion of the pipe materials.
However, for giggles, here is a forum that talks about the same calculations.http://forum.pipeflowcalculations.com/v ... ?f=3&t=218