Recycling rates of aluminum are defined in different (sometimes inconsistent) ways and poorly quantified. To address this situation, the definitions and calculation methods of four groups of indicators are specified for the United States: (1) indicators used to measure recycling efficiencies of old aluminum scrap at the end-of-life (EOL) stage, including EOL collection rate (CR), EOL processing rate, EOL recycling rate, and EOL domestic recycling rate; (2) indicators used to compare generation or use of new with old scrap, including new to old scrap ratio, new scrap ratio (NSR), and old scrap ratio; (3) indicators used to compare production or use of primary aluminum with secondary aluminum, including four recycling input rates (RIRs); and (4) indicators used to track the sinks of aluminum metal in the U.S. anthroposphere. I find that the central estimate of EOL CR varies between 38% and 65% in the United States from 1980 to 2009 and shares a relatively similar historical trend with the primary aluminum price. The RIR is shown to be significantly reduced if excluding secondary aluminum produced from new scrap resulting from the relatively high NSR. In 2003, a time when approximately 73% of all of the aluminum produced globally since 1950 was considered to still be “in service,” approximately 68% to 69% of all metallic aluminum that had entered the U.S. anthroposphere since 1900 was still in use: 67% in domestic in-use stock and 1% to 2% exported as scrap. Only 6% to 7% was definitely lost to the environment, although the destination of 25% of the aluminum was unknown. It was either exported as EOL products, was currently hibernating, or was lost during collection.