First-Class Mail service is an affordable and easy way to send envelopes and postcards. First-Class Mail Forever stamps cost $0.82 (the current 1 oz price) and will never expire, even if the First-Cla

First-Class Mail service is an affordable and easy way to send envelopes and postcards. First-Class Mail Forever stamps cost $0.82 (the current 1 oz price) and will never expire, even if the First-Class postage rate goes up. To send packages, see USPS Ground Advantage service. Mail is delivered in 1–5 days. First-Class Mail is the best-priced service for items up to 13 oz. Features include: one price for up to 3.5 ounces with commercially priced letters and cards; prices based on shape and weight; postmarking and proof of mailing available; proof of delivery through Certified Mail and Delivery Confirmation services. Standard Letter & Postcard Sizes: Standard-sized rectangular envelope stamps start at $0.82. Square, oversized, or unusually shaped envelope stamps start at $1.31. Standard-sized rectangular postcard stamps start at $0.65. Oversized postcards need letter stamps starting at $0.82. Large envelopes (flats) start at $1.69. Weight, Size, & Shape Requirements: Maximum weight for First-Class Mail letters is 3.5 oz; for large First-Class Mail envelopes, the maximum weight is 13 oz. All postcards and envelopes must be rectangular, otherwise an additional charge may apply. Nonmachinable envelopes, unusually shaped mail, lumpy envelopes, rigid envelopes, and mail with clasps, string, or buttons must be hand-canceled and charged a nonmachinable surcharge. Letters exceeding standard envelope maximum dimensions are charged large envelope (flat) prices. Large First-Class envelopes exceeding maximum dimensions or that are rigid, non-rectangular, or not uniformly thick are charged package prices. For businesses, First-Class Mail is targetable, trackable, and measurable. Commercial pricing is available for presorted letters and flats with a minimum quantity of 500 mailpieces. Automation discounts may apply. The page notes specific regulations and standards for mailing restricted, prohibited, and hazardous materials.