How Much Protein? Going by the Numbers

General protein requirements:

The recommended amount of protein for adults is 0.8g/kg or 0.36g/pound.  This is the equivalent of 10-15% of your daily caloric intake.  It is important to note that these numbers are relevant if at least 2/3 of the protein comes from animal sources.

Protein requirements for athletes:

• Endurance Athletes - 0.8-1.4g/kg.  The amount could increase towards the higher number if protein is being used as a fuel source. 
• Resistance-trained Athletes - 1.5-2g/kg.  This is always dependent upon the athlete, the type of protein consumed, and the amount of calories ingested vs. the amount expended.

Concerns:

• Excessively high intakes (greater than 4g/kg) are not advisable, especially for those who have impaired renal function, low calcium intake, or low fluid intake.
• Staying in these protein ranges also keeps nitrogen in balance.

All data from this post is from the NSCA Essentials of Strength and Conditioning textbook, Chapter 10, pages 206-208)