how much he should eat a day?

Question
My lab weighs about 80lbs. and is about a one and a half years old. Is he overweight, underweight, or fine? And how much should I feed him a day?

Answer
Nobody can say without examining the dog.  Go to http://www.longliveyourdog.com/twoplus/RateYourDog.aspx  Depending on your evaluation, increase or decrease how much you are feeding.  Typically what he needs will leave him hungry.  You might ask your vet to confirm your judgment the next time you are in.