If you do a feed bill comparison, assuming that you are not growing out chicks, you will find that your bill on FF is less, and that is with the process of feeding them all they will eat. My flock is in a run due to heavy hawk predation, so their opportunities for free range are limited. I found that my bill on FF is about 25 - 30% less. I fill their dog bowls in the morning, and many days there is still some left in the bowls in evening. You can use the hen's crops to indicate if they are getting enough to eat. If they are not going to bed with empty crops, all is well. Also, feather quality, comb, face, and shank color is a good long term indicator.