Second Ounce Rate (thing)

The "Second Ounce Rate" (which actually is for additional ounces up to one pound) is a United States Postal Service rate for additional ounces on first class mail. It was introduced in 1975, at the same time as another important postal rate change, the end of the air mail rate as a separate rate. Before 1975, additional ounces of weight on first class mail were charged at the same rate as the first ounce. Since then, additional ounces have been cheaper, and over time, the rate has generally drifted downwards in relation to first class postage. Even in absolute terms, it has stayed about the same: in 1988, the price was 20 cents, which is still the price today. Currently, that is about one-third the cost of first-class postage. The reason for it becoming cheaper over time probably has to do with how the economics of how large organizations have changed. The post offices largest expense is probably overhead like employee compensation and capital investment, and the marginal cost of an extra ounce on a letter is probably a relatively minor expense.

Extra ounce stamps are sold as definitives, and are currently forever stamps. Also, the rate for an extra ounce can be completed by adding together different make up rate stamps.

It is also surprisingly difficult to find information on the historical change of the second ounce rate, like other postal prices, and the best source I could find on it was a philately club.