I've just been playing with all this, and if you're going to use a calculator, you need to make a bend that's 90 or more degrees and measure that exacct CLR,
Because the tube srpoings back after you bemd it, the CLR of the bend is almost certain to be bigger than the former, and that can vary from tube to tube.
ERW being different from CFS for instance.
If you're not going to use a calculator, then you need to make a bend that's 90 degrees or more....