First-class mail can be used for postcards, large envelopes (flats), letters and small packages. According to the United States Postal Service (USPS), first-class mail is the preferred method for mailing personal letters, bills and account statements, but can also be used for business purposes, such as sales brochures or shipping light items. Pricing is dependent on the shape and weight of the item to be mailed, with a maximum weight of 13 oz., except for Priority Mail packages which can be heavier.

When to Use First-Class Postage


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Any item meeting size and weight standards can be sent via first-class mail, but the USPS requires all mail that includes personal or personalized business correspondence, handwritten or typewritten contents, bills, credit cards, credit card statements, or any item that is sealed and cannot be inspected, be sent by first-class mail.

First-Class Cards


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To be sent via first-class card rates, postcards must be rectangular, not enclosed in an envelope, printed on cardstock, and at least 3.5 inches high by 5 inches long and 0.007 inch thick, but cannot be larger than 4.25 inches by 6 inches by 0.016. If an item exceeds the maximum dimensions allowed, it will be considered a first-class letter.

First Class Stamp for Letters


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Like first-class postcards, First-class letters must be rectangular, at least 3.5 inches high by 5 inches long and 0.007 inch thick, but no more than 6.125 by 11.5 inches by 0.25 inch. Maximum weight for a first-class letter is 3.5 oz.

First-Class Large Letters or Flats

If a letter exceeds the maximum dimensions allowed for a first-class letter, you can send it via first-class large letter rates. The upper size and weight limits for this classification are 12 inches high by 15 inches wide and 0.75 inch thick and a weight of no more than 13 oz.

First-Class Packages


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If your item weighs 13 oz. or less but doesn’t fit into an envelope, you can mail it via first-class package rates. This classification includes tubes, boxes, padded mailers and thick or large envelopes.

Presorted First-Class Mail

Presorted first-class mail rates apply to bulk mailings of at least 500 identical pieces, each weighing no more than 13 oz. Different rates will apply depending on size and weight, with mail being classified into the standard categories of cards, letters, large letters and parcels.

As the name implies, mail must be presorted by destination zip code, marked for presort pricing, and may require a bar code if the item weighs 3 oz. or more.

First-class Priority Mail


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Priority Mail is a special type of first-class mail used for packages over 13 oz. Both flat and metered rates are available. Flat-rate shipping can be used for any item or items that fit in the USPS’s prefabricated flat-rate packages. In order to get the flat-rate price, a USPS Flat-Rate box must be used. Metered Priority Mail rates are determined by weight and destination zone. Priority Mail will generally reach its destination in two to three days.