The current recommendation is that bodybuilders and athletes should take in 1.8 grams of protein/kg of bodyweight, but this study found greater gains in subjects taking in 2.8g protein/kg bodyweight. If you’re trying to optimize muscle growth, shoot for 2-3g protein/kg bodyweight to maximize gains.
Willoughby, D. S., Stout, J. R., & Wilborn, C. D. (2007). Effects of resistance training and protein plus amino acid supplementation on muscle anabolism, mass, and strength. Amino Acids, 32(4), 467-477.