Backing into head loss calculation?


Well-known member
May 25, 2007
I had a thought I wanted to throw out for discussion.

Assuming one has a clean filter, an accurate head loss graph and weighs a gallon of pool water, do you think it's possible to hook up a hose to the return then put the end of the hose in to a container for 5-10 seconds, weigh the total amount then divide by the gallon of pool water result to get gallons flowed during the 5-10 seconds, multiply to calculate GPM, pick this point on the pump curve line then intersect for head loss?

My pool has one return. On a pool with multiple returns I assume you can shut them down for the test, or some additional calculation would be needed to get an accurate result?


TFP Expert
LifeTime Supporter
May 3, 2007
Pleasanton, CA
It would probably be close enough but you need to make sure the extra line does not cause a significant amount of head loss itself. A line much larger than the plumbing should be ok.

Also, turning off returns changes head loss as well so that will create error. So if you have multiple lines you will have to test each one individually and sum for the total flow rate.

Water weighs 8.34 pounds per gallon but you don't really need to do that. Just use a large 5 gallon bucket and time how long it takes to fill it.

The best way to measure is with a flow meter but that requires a plumbing change. The second best method uses filter pressure and suction measurement at the pump to determine head loss and a look up of the flow rate.


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
If done carefully that test seems reasonable, but it isn't going to be easy to do for most people. A basic flow meter can be had for less than $100, is probably easier to install than running that test, and will show you the flow rate constantly for years to come.