Spastic, you are certainly not a bad horsey mom LOL. I don't weigh my hay at all. I judge by the quality of the hay, the appearance of the horse, how quickly they finish what I give them, etc.
Like right now with my horses that are being fed in meals instead of free choice, I have 2 that get much less as they are both fat and don't seem to need as much food since they usually have a bit left over at the next feeding so they get 1 flake per meal. Another one eats slowly but unless she gets at least 1 1/2 flakes a meal (3x3 flakes), she starts to get ribby. The last one is a vacuum cleaner and a pretty hard keeper. He requires at least 3 flakes per feeding or he drops weight like crazy. The bales themselves average about 800 pounds and I would say that a flake would weigh 10-20 pounds depending on the bale.