How much should, on an average, a six month old baby weigh?

I know everyone is different, but how much on an average, Also, how big should their head be?How much should, on an average, a six month old baby weigh?
a baby doubles their birth weight at 6 months and triples it at 12 months. on average.
I dont remember what he weighed at 6mths but , He weighed 5lbs at birth and 18 lbs at one yr. At 16, he weighs 175!! lol I never measured his head.