Code Golf Measurer © 2019
Retina 0.8.2, 8 bytes

.{51}

.


Try it online! Explanation:

.{51}


Delete the first 51 characters of each line. (Lines can only have between 52 and 67 characters, so this always matches once per line.)

.


Count the remaining non-newline characters.

7 bytes if empty input did not have to be supported:

.{52}




Try it online! Explanation:

.{52}



Delete the first 52 characters of each line. (Lines can only have between 52 and 67 characters, so this always matches once per line.)




Count 1 more than the number of remaining characters (including newlines).