1. Measure the length in inches from lower jaw to the fork of the tail.
2. Measure the girth in inches at the widest part around the body.

The total length is the maximum length of the fish, with the mouth closed and the tail fin pinched together.

Most marine (saltwater regulations) refer to the "fork length", and scientists often use "standard length" which is to the end of the fleshy part of the body. "Standard length" has the advantage of not being affected by minor damage to the tail fin, nor does it give too much credit to a fish for the relatively light weight tail when calculating a fish's condition.

"Girth" can be determined by drawing a string around the fish at its widest point marking where the string overlaps and then measuring the distance between the overlapping points on a conventional ruler. The measurement should be taken perpendicular to the length of the fish.  This measurement is analogous to measuring the circumference of someone's waist. Knowing the girth is important when trying to certify a fish for a record.

For "The One That Got Away" you can tell a fish story and use your imagination. :)

Take a kid fishing:

The biggest thing to know about taking a kid fishing is that it is about spending quality time together.  Try to avoid putting pressure on yourself or the kid by expecting to catch lots of fish or especially big fish--remember they call it fishing, not catching, for a reason.  Fishing provides a great time to find out what the child is interested in and just talk.  But if the subject shifts to fishing, talk about the history of fishing, what fish need to survive and how important clean water and healthy habitats are to fish and people.  These discussions can lead to fun expectations, but fulfillment isn't always instantaneous, so patience is the key for both you and the kid. Be sure to tell the kid about the one that got away.