In 2009, the United States Post Office handled approximately 6,671 pieces of mail every second. About 40 percent of the world's cards and letters are handled by the USPS. Postage rates are set for standard-sized mail pieces and anything that doesn't fit into the standard categories is subject to additional charges.


Before 1847, the postmaster hand wrote postage in the corner of every letter. The USPS began using pre-printed stamps when it bought the "City Despatch Post," a private carrier that created the stamps in 1842. At first, postage was weight based with little concern for size. However, as volume increased, the USPS began using mechanical readers and sorters. In 2009, the Automated Flat Sorting Machine could sort 17,000 pieces of flat mail per hour. To make the best use of technology, the post office standardized envelope sizes. Anything outside the standard size is considered nonmachinable and is subject to a surcharge.

Small Envelopes

In 2011, postage for a 1 ounce letter in a standard small envelope was 44 cents. A standard small envelope is between 3 and one-half inches and 6 and one-eight inches tall; between 5 inches and 11 and one-half inches long and no more than one-quarter of an inch thick. The maximum weight is 3 and one-half ounces. A nonmachinable surcharge of 20 cents is added if the envelope is square, is too rigid, has clasps or has an uneven surface such as an envelope containing coins. A letter is also nonmachinable if the length divided by the height is less than 1.3 or greater than 2.5.

Large Envelopes

In 2011, postage for a 1 ounce letter in a standard large envelope was 88 cents. A standard large envelope is between 6 and one-eighth inches and 12 inches tall, between 11 and one-half inches and 15 inches long and no more than three-quarters of an inch thick. Large envelopes that are not rectangular, not uniformly thick and do not meet the flexibility requirements are charged the price for packages.


The phrase "First-Class Mail" is a registered trademark of the USPS. Issued in 2008, the registration number is 3796195. Before 1974, as many as 20 percent of all postage stamps were soaked off and reused. The longest regular mail route is 176.5 miles per day to deliver to 174 mailboxes in North Dakota. In Tulsa, Okla., the airport post office is open 24 hours a day, 365 days per year.