As of the end of 2019, the total market capitalization of the S&P 500 was $26,759,686,786,884. Or, if you prefer, approximately $26.76 trillion!
That's 14.8 times the value of the S&P 500's market capitalization at the end of 1988-Q1, when the index's market cap stood at $1.81 trillion. From 1988-Q1 to 2019-Q4, the S&P 500's total market capitalization has doubled three times, completing its first doubling period in 7 years from 1988-Q1 to 1995-Q1, taking another 2.5 years to double again by 1997-Q3, and then another 16 years to double a third time in 2013-Q3.