As of October 2014, the postage rate to mail a first-class, letter-size envelope through the United States Postal Service is 49 cents for the first ounce. For large first-class envelopes, the rate is 98 cents for the first ounce. Each additional ounce per envelop costs 21 cents. The USPS charges a penalty of 21 cents if the post office scanner cannot scan the envelope.
Letters more than 1/4 inch in thickness are considered large envelopes. Large envelopes exceeding 3/4 inch in thickness are weighed as packages. An envelope is also considered large if its length exceeds 11.25 inches or its height is greater than 6.125 inches.
USPS also uses zones to calculate mail rates. Zones are determined by the distance a piece of mail travels to reach its destination. For example, mail traveling from California to Maine is considered a zone seven item. USPS provides a zone chart specific to the originating zip code.
In addition to standard postage, USPS offers free electronic tracking for priority mail, parcel and select first-class package services. Certificates of mailing, certified mail, collections on delivery, notices of non-delivery, registered mailing, restricted delivery, return receipts, signature confirmations and special handling are available for additional fees.