My question is, I am keeping our sons full grown e Mastiff for a while and have been feeding him 16 0z of Dry with 1 can of Pedigree in the am and 8 oz of dry and I/2 can soft food in the evening. Is this enough ?
How much to feed has several variables. But the quick answer is to look at the can/bag, it should have feeding instructions for dogs based on their weight for the quality of the food.
That is a guideline, if the dog is getting fat or skinning then you adjust the food accordingly. Your vet should tell you what a healthy weight for your dog is during your regular visits.