It occurs to me that pressure is not the same as volume or flow in this circumstance. Capping the line creates a closed system and the pressure will be the same throughout. So how do I measure flow? Run the water into a bucket for 1 min and then measure how much? Any help would be apreciated.

This post was edited by syd81 on Fri, Aug 1, 14 at 12:58

You are correct, you cannot measure the flow rate the way you proposed in first post.

You won't get a good approximation without the finished fixtures in place. Most of them have flow rate restrictors.

You probably need to look at what size pipe, how long, how many el's to come up with a pressure drop for a given run. That will give you a better idea

is this a "new" bathroom or a remodel of an existing?

It is a new bathroom. I ran the lines myself and didn't consider running 3/4 at the time - only later to read about problems with long runs. It is a second floor bath.

Would it be a matter of hooking up the fixture, measuring the gpm, and then comparing it to the manufacturer recommendation?

How long is the run, how many elbows, how many fixtures, what kind of pipe (pex, copper, CPVC)?

Short of doing the math... you may run into an issue if have multiple fixtures (shower, sink, toilet) on a single half inch run. What you will have is the shower changing temp when the toilet flushes, for example. Half inch is usually fine for single fixture in residential applications.

As far as a single use- you are most likely to see any problem in the tub - where the flow isn't restricted.