Determine needle size

I have some circular needles that I am trying to figure out the size. When I use a needle gauge does the needle need to go through the hole completely or does it stop at the end of the taper where the needle becomes wide?

Generally the shaft of the needle should go through the hole. I have some that just don’t quite go through but are too small for the next larger size. Needle gauges can vary also. IME it’s whatever is closest to the needle shaft just sliding through is the size to go with.