length guides

I've heard a rule of thumb is to feed my beardie locusts no bigger than the length between his eyes, i was wondering if that means the length of the locust has to fit between his eyes, or the width of the locust has to fit between his eyes. i'm about to buy a beardie (6 months old) and need to...

my baby corns are about 30cm ( i think) when do i start giving them double feeds on pinky's? does anyone have an estimate length guide for when to up their feed? example - 30cm = 1 pinky or 60cm = 2 pinky's i hope this explains what i mean. any suggestions will be a great help, im new at this!