They are always a bit larger than you think. Even the ones bobbing along near the trails. Their tail may be the biggest part of their body. And it’s fairly hefty since it’s for swimming, splashing, and general mobility.
Here is one that is probably twice the size I originally thought… still a young one though.
The old rule is to check the distance from their nose to head. Estimated inches is equal to feet. So, a 6 inch nose is a 6 foot Alligator.
I’m not sure how accurate that is but when all you see is a head it’s better than nothing.