The method listed on poolplaza is the only way to accurately figure your TDH. You can only do it once everything is up and running though. Trying to do it before hand based on the number of elbows, feet of pipe etc is too difficult and will probably not provide the right answer anyway. Most in ground pools have a TDH of 50-60'. Just use that number and you will be close enough.

Brad
Waterworks Pools