The RDA is .8 grams per kilogram of bodyweight.
HOWEVER, a very recently published University study, as repoted in Jerry Brainum's excellent and well researched Bodybuilding Pharmacology column in Iron Man, showed otherwise.
The study followed power-lifters and athletes training a minimum of five times a week using heavy resistance training for a minimum of one hour. It tracked protein synthesis, maintenance of an anabolic state, and lean mass as well as strength gains, including doing muscle biopsies of all subjects, including a control group.
What was published suggests the following:
1.4 grams per kilogram of LEAN body weight was the maximum amount that was utilized and beneficial. Less showed slightly lower gains in strength and mass, and more showed no significant difference whatsoever.
It also de-bunked concerns over excess protein doing damage to healthy kidneys. The excess is simply wasted in the liver, where it's burned off to no deleterious effect.
The study also showed strong evidence that consuming more than 20 to 25 grams per meal was a waste (only a few subjects appeared to synthesize as much as 25 grams per meal, but the number was small.)
The research also showed that ANY carbohydrates consumed within 2 hours of a heavy workout directly benefited protein synthesis. So carb up after the workout without fear would the implication.
However, the previously accepted window of 30 minutes for consumption of protein after a workout, dropped to 20 minutes, so drink up and drink up fast, men!
So what does this mean if you're a Real Jock lifter who does train hard and heavy five times a week, and say you're 5'10" have a target weight of 170 pounds and 8% bodyfat? You need 190 grams a day. Here's what you'd have to consume and how:
6 A.M. Protein Shake (20 grms)
8 A.M. Breakfast with 4 egg whites (19 grms)
10:30 A.M. Pre-Lunch of a 4 oz chicken breast (25 grms)
1 P.M. Lunch of 4 ounces of white fish like Perch (20 grms)
3 P.M. Pre-workout shake (two hours before workout) (20 grms)
6:30 P.M. Post-workout shake (20 grms)
8 P.M. Dinner of 4 oz chicken breast (25 grms)
10 P.M. After-dinner Casein protein drink (20 grms)
Total of eight 'meals' - and still only 170 grams of protein - the remaining 20 grams is filled in through other foods, like beans, rice, some cereal, whole grain breads, certain fruits and nuts like almonds, and most likely will exceed the 190 required/suggested.
If you're not looking for size, but still want more muscle than you have, then the article suggests 1.25 to 1.3 grams per kilogram, so using the same Real Jock as above the intake would drop to about 170 grams a day.
Mind you, there are other recent studies that show the more protein intake the better, so long as you're lifting serious weight and looking for very serious size and strength gains = like a powerlifter or competitive drug-free bodybuilder.