| Domestic Letters | ||
| Effective Date | Per 1/2 ounce | |
| March 3, 1863 | 3 | |
| March 3, 1883 | 2 | |
| Per ounce | ||
| July 1, 1885 | 2 | |
| November 3, 1917 | 3 | |
| July 1, 1919 | 2 | |
| July 6, 1932 | 3 | |
| August 1, 1958 | 4 | |
| January 7, 1963 | 5 | |
| January 7, 1968 | 6 | |
| May 16, 1971 | 8 | |
| March 2, 1974 | 10 | |
| First Ounce | Each Additional Ounce | |
| September 14, 1975 | 10 | 9 |
| December 31, 1975 | 13 | 11 |
| May 29, 1978 | 15 | 13 |
| March 22, 1981 | 18 | 17 |
| November 1, 1981 | 20 | 17 |
| February 17, 1985 | 22 | 17 |
| April 3, 1988 | 25 | 20 |
| February 3, 1991 | 29 | 23 |
| January 1, 1995 | 32 | 23 |
| January 10,1999 | 33 | 22 |
| January 5, 2001 | 34 | 23 |
| June 30, 2002 | 37 | 23 |
| January 8, 2006 | 39 | 24 |
| May 14, 2007 | 41 | 17 |
| May 12, 2008 | 42 | 17 |
| May 11, 2009 | 44 | 17 |
| April 17, 2011 | 44 | 20 |
| January 22, 2012 | 45 | |