Sometimes it is an indicator, and sometimes my smallest runt will end up being a hen. When the chicks are 2+ weeks old, I’ll often start seeing differences in size and shape. More often than size, shape is an indicator. It’s a subtle difference, but males are more torpedo shaped, and hens are wider, especially in the breast. Still it’s not definite, because chicks go thru awkward growing stages. most recently, my only black chick from the k dale eggs ended up being a hen, even though she was the smallest in her hatch. I have one of her chicks now in the brooder, at 2 weeks it’s looking male so far and I have my fingers crossed for it to be male, but it could be a tiny hen like the mom.