Does anyone know a healthy or ideal weight for a ferret?

I have 3 males and 2 female ferrets and they've put on weight during the winter (Entirely my fault).Does anybody have an idea of the ideal waistline measurement or the range or weight for both a dog and jill? Or even your own ferrets measurements? I know it will change with each individual but im reducing there diet slowly and monitoring their weight loss but want to get an idea of how overweight they actually are. I will ask the vet the next time im in but that might not be for a couple of months.Thanks

Male Ferret: average 3 - 5 lbs, 17 - 24" length (1.35 - 2.25 kg and 43 - 61 cm) Female Ferret: average 1 - 3 lbs, 12 - 16" length (0.45 - 1.35 kg and 30 - 40 cm) I also noticed that during winter my Ferret tends to gain weight and during summer he tends to be more on the slim side. My Ferret is a male and i recently weighed him and he weighs 3.4pounds.