As I researched this topic, I found many Americans eat way too much protein (well, we eat too much period).... But, here is a great excerpt from WebMD:
How Much Protein Is Enough?Adults in the U.S. are encouraged to get 10% to 35% of their day's calories from protein foods. That's about 46 grams of protein for women, and 56 grams of protein for men.
It's not hard to get this amount if you eat two to three servings of protein-rich foods a day, according to the CDC.
There are some people that need more protein and it discusses that further: