Ideally you should get around at least 1 gram per pound bodyweight. You need protein to provide your muscles with the building blocks it needs to grow and repair. Don't think if you eat 500 grams of protein a day you will gain muscle twice as fast than eating 250 grams. Your body can only synthesize a certain amount of protein daily,after that it is either stored as fat or excreted as urea. This is determined by genetics and hormone levels. Why do you think pro bodybuilders get so big, they take hormones e.g testosterone to increase protein synthesis... they can expect to grow more on extremely high protein diets.