Formula for current through shift register
It's just N×IL+IQ where N is the number of LEDs, IL is the current through each LED and IQ is the current the shift register needs to operate (quiescent current).

The current through each LED is just (VIN - VLED) ÷ R, where VIN is 5V, VLED is the forward voltage drop of the LED, and R is the value of your resistor.

So you can combine it to be a single formula, if all your LEDs are the same and your resistors are the same, to:

IT = N × ((VIN - VLED) ÷ R) + IQ