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Mail Classes and Services

An overview of the various mail classes and services offered by the United States Postal Service.

Note: In this document, "mail" refers to anything sent via USPS. This includes letters, envelopes, boxes, tubes, etc.

Domestic vs International

All mail falls into one of two categories: domestic mail and international mail.

Domestic mail is sent and received within the United States. It is delivered by USPS. This includes U.S. territories (such as Guam or Puerto Rico), U.S. possessions (such as Micronesia), and U.S. military bases and ships around the world.

Domestic mail usually doesn't require any special paperwork like customs forms, and prices are either a flat rate (the same price no matter the distance it travels) or are priced by zone, which is a number from 1 to 9. The larger the zone number, the farther the mail must travel, and the more it costs to send.

International mail is mail sent from the United States to a foreign country. It is delivered by the destination country's own postal service. A customs form is usually required, except for letters. International pricing is based on the destination country, with different countries falling into one of 20 price groups (which work similar to domestic mail zones).

Domestic Mail Services

There are several "classes" or "services" of mail provided by USPS. Mail is usually priced by the weight and distance from origin to destination, although some exceptions exist such as First-Class Mail (priced by weight only) and Flat Rate packaging (one price regardless of weight and distance).

First-Class Mail: Letters, Envelopes, and Postcards

  • Delivery in 1-5 days
  • Same price regardless of distance
  • For letters and envelopes
  • No tracking included

Shapes

First-Class Mail has several different "shapes" of mail, with different pricing.

All mail must be at least 3½ inches tall by 5 inches wide. Smaller items will be returned to sender as nonmailable.

  Postcard
    Thickness: 0.007 inch to 0.016 inch (typically, the thickness of cardstock)
    Minimum Size: 3½ inches by 5 inches
    Maximum Size: 4¼ inches by 6 inches

If a postcard is too large, it needs to be mailed as a letter.

  Letter
    Thickness: 0.009 inches (the thickness of thick cardstock) to ¼ inch
    Minimum Size: 3½ inches by 5 inches
    Maximum Size: 6⅛ inches by 11½ inches
    Maximum Weight: 3.5 ounces

If a letter exceeds one or more of the size or thickness maximums, it is moved up to a Flat, or large envelope. However, if it does not meet the flexibility and shape requirements for a Flat, it must be mailed via a parcel (package) service.

A letter is considered "non-machinable", that is, subject to a non-machinable surcharge if it:

  • is square,
  • the length divided by the height is less than 1.3 or greater than 2.5,
  • has an outer surface that isn't paper,
  • is closed with a clasp, button, or string,
  • is rigid (stiff),
  • contains items such as pens, keys or coins that cause the thickness of the mailpiece to be uneven, or
  • has the delivery address not parallel to the long side.

  Flat (large envelope)
    Thickness: ¼ inch to ¾ inch
    Minimum Size: 6⅛ inches by 11½ inches
    Maximum Size: 12 inches by 15 inches
    Maximum Weight: 13 ounces
    Must be flexible, rectangular, and uniform thickness: Rigid and stiff items are not allowed. Flats must also be rectangular or square. Any variations in thickness (bumps, dips) must be less than ¼ inch high or deep.

A flat must meet at least one of the size minimums (length, width, or thickness). It must be smaller than all the size maximums. If a flat exceeds one or more of the maximums, it is a parcel (package).

If a flat isn't flexible, rectangular, and uniform thickness, it is a parcel.

Ground Advantage

  • Delivery in 2-5 days
  • For parcels (packages) up to 70 pounds
  • Price based on weight and distance (zone)
  • Four price tiers for lightweight parcels: up to 4 oz, up to 8 oz, up to 12 oz, and up to 15.999 oz
  • Per-pound pricing for parcels from 1 pound up to 70 pounds
  • Tracking included

Priority Mail

  • Delivery in 1-3 days
  • For parcels and envelopes up to 70 pounds
  • Price by pound and zone
  • Tracking included

Flat Rate

USPS produces several Priority Mail Flat Rate boxes and envelopes with a red and white color theme. Unlike other packages, Flat Rate items cost the same no matter the weight or distance. The price is instead based on the specific packaging used.

Flat Rate packaging:

  • Flat Rate Envelope: several variations available, but up to 12 1/2 by 9 1/2 inches they are all the same price.
  • Flat Rate Legal Envelope: 15 by 9 1/2 inches
  • Padded Flat Rate Envelope: 12 1/2 by 9 1/2 inches
  • Small Flat Rate Box: 8 11/16 by 5 7/16 by 1 3/4 inches
  • Medium Flat Rate Box: Two sizes available: 11 1/4 by 8 3/4 by 6 and 14 by 12 by 3 1/2
  • Large Flat Rate Box: 12 1/4 by 12 1/4 by 6 inches

Other Priority Mail packaging:

USPS also produces many other sizes of Priority Mail shipping boxes. Unless the box has "flat rate" printed on it, it is priced by weight and distance.

USPS-made free packaging must only be used for the mail service printed on the packaging.

Priority Mail Express

  • Delivery in 1-2 days
  • Guaranteed service (except items going to or from Alaska or Hawaii)
  • For parcels and envelopes up to 70 pounds
  • Price by pound and zone
  • Tracking included
  • Optional signature add-on is free

Flat Rate

As with Priority Mail, Priority Mail Express has several Flat Rate envelopes. The Express envelopes have a blue and white theme. However, there are no Express Flat Rate boxes.

Media Mail

  • For books, DVDs, and certain other media.
  • Price by pound, no matter the distance
  • Tracking included
  • May be inspected by USPS to ensure contents meet eligibility requirements.

Media Mail eligibility rules can be found in PostalPoint (Ship page, Options tab, under Special Rates) or at https://pe.usps.com/text/dmm300/173.htm#ep1113500

International Mail Services

First-Class Mail International

Service is generally the same as domestic First-Class Mail, except:

  • Flats can weigh to 15.994 ounces
  • There is no international postcard rate; postcards must be mailed as a letter

The price for a 1 ounce letter or flat is the same for all destination countries, but prices vary by destination for items over 1 ounce.

First-Class Package International

  • Packages up to 4 pounds (64 ounces)
  • For parcels, the length (longest side) between 6 and 24 inches; height at least 4 inches; combined length, height, and width up to 36 inches
  • For rolls/tubes, the length must be between 4 and 36 inches, and the length plus twice the diameter must be between 6 3/4 inches and 42 inches
  • Tracking included (delivery confirmation only available in certain countries)

Priority Mail International

  • Delivery in 6-10 business days
  • Up to 70 pounds
  • Tracking included
  • Up to $200 insurance included ($100 for document reconstruction, $200 for merchandise/gifts/goods)
  • Flat Rate options with pricing based only on country, not weight (max of 4lbs for envelopes and Small Flat Rate Box, max of 20lbs for Medium and Large Flat Rate Boxes)
  • Some countries have lower weight limits

Priority Mail Express International

  • Delivery in 3-5 business days
  • Up to 70 pounds
  • Tracking included
  • Up to $200 insurance included ($100 for document reconstruction, $200 for merchandise/gifts/goods)
  • Flat Rate envelope options with pricing based only on country, not weight (max of 4lbs)
  • Some countries have lower weight limits

Extra Services

USPS offers several extra add-on services which can be combined with most mail services to add additional features.

Insurance

  • Insures the item against loss or damage while in USPS possession, with some limitations
  • Available in any amount up to $5,000
  • Ground Advantage, Priority Mail, and Priority Mail Express include $100 of insurance for free, but extra coverage can be purchased when creating the shipping label

Signature

  • Requires a signature on delivery
  • Adult Signature variant requires the signer be 21 or older

Certified Mail

  • Requires a signature on delivery
  • Adds tracking to First-Class Mail
  • USPS refunds Certified Mail fee if no signature is collected within 30 days

Registered Mail

  • Requires a signature on delivery
  • Mail is sealed in tamper-evident packaging and travels in locked containers
  • For high-value shipments, such as coins, jewelery, cash, or confidential documents
  • Requires the sender to declare the item's value when mailing

Restricted Delivery

  • Combines with Certified Mail or signature service
  • Requires the mail be personally received by the person it's addressed to (addressee) or their legal agent (i.e. power of attorney)