"The estimate, from the Centers for Disease Control and Prevention, is based on serology testing used to determine the presence of antibodies that show whether an individual has had the disease, the officials said.

The officials, speaking to a small group of reporters on Wednesday night, said the estimate was based on the number of known cases, between 2.3 million and 2.4 million, multiplied by the average rate of antibodies seen from the serology tests, about an average of 10 to 1.

“If you multiply the cases by that ratio, that’s where you get that 20 million figure,” said one official."

And I realize it's not your chart but you posted it and are defending it.