| Pop Radio Top 20 History | |
| 7/12/1940 - 10/25/1955 | Based On Billboard Best Sellers Chart |
| 11/4/1955 - 7/25/1958 | Based On Billboard Top 100 Chart |
| 8/1/1958 - 9/28/1973 | Based On Billboard Hot 100 Chart |
| 10/5/1973 - 1992 | Based On Radio & Records CHR Chart |
| 1993 - 4/15/1994 | Based On Billboard Mainstream Top 40 Chart |
| 4/22/1994 - 8/4/2006 | Based On Radio & Records/Mediabase CHR/Pop Chart |
| 8/11/2006 - Current | Based On Mediabase Top 40 Chart Data |