usps max weight of letter
Lets answer your question in several parts; The Short Version First: 1: First Class Letter - Max weight is 3.5 oz 2: First Class Large Envelopes - Max weight is 13 oz 3: First Class Parcels - Max weight is 13 oz Long Version: 1.
With the United States Postal Service (USPS), one first class stamp buys you 1 ounce of postage, assuming you are using a regular-size, rectangular envelope. cf: Current Postage Rates, US Postage Stamp Prices.