How can you estimate the length of an alligator?

It is very hard to estimate the size of an alligator buyt one rule of thumb that comes close is that their length is usually very close to the distance between the eyes measured in inches can be used, just convert the inches to ft. ie: 8 inches= 8 ft. (the question then becomes, how accurate are you at estimating the distance between the eyes) (Discussion) I've heard this rule before but another rule is also out there. The distance from the eyes to the end of the snout. That seems a little more believable but I don't know for sure. Also, where is the start or stopping point for these locations?