When I first started breeding a number of years ago, my broodie ran into problems and had to be shipped with her foal to Cornell. The colt was just barely 2 days old and he weighted 125 pounds! Better yet, his dam, a 16.2 hand TB weighted 1700 pounds! yes, I made them weigh her again and it was accurate.
So I use that first hand knowledge to judge my other babies. My mares do have large foals and typically they are about 10+ hands and over 100 pounds at birth. I can lift 75-80 pounds and carry it. I can't do it with something over 100 pounds b/c our old dog was 135 pounds and I could not carry him. I have never been able to carry one of our foals, even the rare petite ones.
Now I have had some whoppers too. I have a coming 2 year old WB filly who when born was 11+ hands and easily weighted close to 200 pounds, this out of a 15.1 hand (tank of a) mare. This filly will be 2 on May 31st of this year. She is currently 16 hands and wears a 72 inch blanket with ease. She may make 17 hands like her sire, my stallion. I still thank God every day Finally, the filly, learned to lead at such an early age b/c when she set her feet and did not move I could not move her! Heck two people struggled to move her forward.
When I bred my Arab mare, her 2 foals were about 75# each at birth. In 2009 I had to pull my Oldenburg colt from his 16 hand mum. When we got him out, he was exhausted. We got he and mum to MSU so he could be tube fed and they put him on the scale first. I saw them start whispering into their walkie-talkies "you've got to come see the size of this baby". lol, he was 165# even dehydrated and exhausted. That is my second one that size. He is 15.3 at 18 months and my other one that was that size is 17.1 at three.
I'm really really ok with the smaller ones, the big ones are soooo hard to get up.