Genden .... ITA with the others.
Find your "body" measurement, that works for you, so you don't need a ruler!
I'm also thinking you may be asking about the other "how to" for quilting distances .....
The 3" requirement is in all directions ...... left-right-up-down
IOW, it is not a 3" channel across the width of a quilt, but quilting is needed within that channel.