Originally Posted by its lbs not miles
A reasonably accurate way I was taught by some old timers (people who are or would be 85+ years now) is to measure the distance from the coronet band (top of the hoof) up to the center of the knee (just above the cannon bone).
Every inch's equal to a hand, or a 1 to 4 ratio (one inch = four inches). If the distance was 14.25" you could estimate the horse to reach 14.1 hands.
Not saying it's always 100%, but it has often been pretty close.
See, I don't think this works. I tried it on Aires and got between 17.1-18" (bugger kept moving around and trying to see what I was doing, so I had to measure four times and got a different measurement each time). Right now he's right around 15.2-15.3hh (closer to 15.3hh) and two-years-old. Someone said that at two they are 97-98% of their adult height (something like that). So, by the string test, he'll turn out in the 17-18hh range. By the other reckoning (based on him being 97-98% of his adult height), he'll top our at maybe 16.1hh.
Also, I tried the method where you measure with a lead rope from fetlock to elbow, then invert the lead rope and measure from elbow up and wherever the end of the rope falls above the withers is how tall they'll be. By that, again, he'll be around 17hh.
Sorry, not meaning to go OT, but just maybe trying to warn the OP that these methods are often more confusing than they are helpful.