USPS 

https://www.usps.com/ship/mail-shipping-services.htm

If you’re selling products online, it’s important to understand the difference between The United States Post Office’s First-Class and Priority Mail shipping solutions. Using the right service can save you money on your shipping costs, ensure that your packages arrive on time, and instill trust in your customers.

Are you ready to become a smart shipper? Take a look at our quick-start guide below, then print out our infographic Master Cheat Sheet for USPS Shipping.

First-Class Mail

First-Class mail is intended for lightweight letters, flats, and parcels. Shippers are charged at a per-ounce rate and can expect that mail will be delivered in 1-3 days.

Letters:

Letters are classified as flexible envelopes that weigh 3.5 oz or less, have maximum dimensions of 6.12 x 11.5 inches, and are not thicker than .25 inches. Letters mailed First Class will not have delivery confirmation.

Flats:

Flats are classified as large or padded envelopes with minimum dimensions of 6.12 x 11.5 inches, maximum dimensions of 12 x 15 inches, and a maximum thickness of .75 inches. Flats mailed First Class will not have delivery confirmation.

Parcels:

Parcels are classified as rigid boxes that are at least .75 inches thick, but still weigh less than the First-Class limit of 13 oz. Unlike letters and flats, First-Class parcels do qualify for delivery confirmation.

On January 22, 2012, the USPS implemented prices changes to First-Class mail that place packages into two different categories:

First-Class package service:

This service is intended for commercial customers, including those using PC Postage. Free tracking and delivery confirmation is included in this service, but packages cannot contain any personal correspondence. Keep in mind—this is one of the few postal mail classes that the USPS can legally inspect.

First-Class mail parcel:

This is a retail-priced service intended for private, rather than commercial, shippers.

Priority Mail

Priority mail is the optimal choice for heavier products, because shippers can send packages weighing more than 13 oz at an affordable rate. Priority Mail also offers the option of using free Flat Rate boxes or envelopes, which is a good solution for shippers who don’t own a postage scale. 

Priority mail will be delivered in 2-3 days (a faster option than Parcel Post or Parcel Select), and PC Postage users will receive free delivery confirmation. Delivery confirmation is especially important for eBay sellers, as a new mandate requires that top-rated sellers have to provide tracking information for at least 90 percent of their orders.

Priority Mail also includes Regional-Rate boxes, a commercial solution geared toward PC Postage users that charges based on shipping zone and weight tier.  Shippers can use Regional Rate boxes for products weighing up to 15, 20, or 25 lbs.

Flat-Rate and Regional-Rate boxes and envelopes are available for free from the USPS online store.

For more information about dimension limits for First-Class, Priority, and Regional-Rate mail, visit the USPS website.