Man
Deer
Hog
Elk
Horse
Cow
Telephone pole
Fence post
Man? 5'9" unless he is more or less. How do you know you are seeing the average?
Deer? Buck, Doe, what part of the country? North Texas deer much larger than central Texas deer.
Hog? LOL. How do you know the difference between a 100 lb hog at 200 yards or a 200 lb hog at 400? Hogs vary considerably in size and weight.
Etc.
There is a lot of guessing going one with a lot of the "averages," particularly with wildlife, that could have considerable influence on your ranged results.
A laser rangefinder (as noted) will save you a lot of time and hassle if you are planning on making accurate hunting shots.