Roughly 1 gram of protein per poundofbodyweight per day has been reliably shown many times to be a near optimal amount (actually, a bit less than 1 gram seems to be optimal, but 1 gram keeps the math easy).
This may seem exceptionally low to some, particularly strength athletes who are used to taking in 2 - 3 grams per POUNDofbodyweight, but is the reality.