Assuming your brand of bender uses the minimum radius of bends (most do) the NEC indicates that that figure is 4.5" for 3/4 pipe.
The "length" of the bend is then 4.5", but the length of pipe used to make that bend is 3.14*4.5/2, or 7". The "loss" is then 7-4.5, or 2.5". This is all assuming that the pipe is a pencil line, not a 3-dimensional object, which we know is not true. You would have to check in practice, but I suspect that the NEC figure is to the inside of the bend, meaning that the loss will be 3/4" less than what is calculated: the length of the completed bend will be 3/4" more than the minimum radius.
Why not just use the star on the bender rather than the arrow?