USPS Postage Calculator

Access the lowest USPS postage rates with ShipStation. Get a quick estimate with our USPS postage calculator today!

ShipStation gets you the best USPS Postage Rates

ShipStation offers affordable USPS postage thanks to our close relationship with USPS postage provider These rates do not require you to ship a certain volume of shipments. You get the same great discounts if you ship one package with ShipStation or 10,000.

Use our rate calculator to streamline your shipping process and always choose the lowest shipping rate for any and all of your packages. We also offer discounts and integrations with many of the world’s top carriers.

Find the Cheapest Options: USPS First Class Mail

First Class Mail is the cheapest way to ship a package weighing less than 16 oz with dimensions less than 22″ x 18″ x 15″ in maximum length. If the parcel exceeds 16 oz or has dimensions exceeding this size, you will need to use USPS Priority Mail. USPS First Class Mail also supports letters, envelopes, thick envelops, flat rate envelopes, and postcards.

First Class Mail also supports international parcels weighing up to 4 lbs. To find available international rates as well as other carriers’ rates, sign up for a free 30-day ShipStation trial now!


What is the best way to send items weighing less than one pound?

USPS First Class Mail is the most economical shipping option for any parcel weighing less than 16 oz. First Class Mail offers tracking and quick delivery times comparable to Priority Mail.

What is the best way to send items weighing more than one pound?

USPS Priority mail offers an affordable option for sending items weighing 1-10 lbs. For some parcels in this weight range being shipped to further zones as well as even heavier parcels, UPS and FedEx Ground offer affordable rates to quickly ship your parcels within the US.

How large can an envelope be and still be eligible for First-Class Mail letter rates?

USPS First Class Large Envelopes and Flats can have a height ranging from 6 ⅛” and 12”, a length between 11 ½” and 15”, and a thickness of ¼” and ¾”. The maximum weight for a First Class Large Envelope or Flat is 13 oz.

How is USPS Postage calculated?

A parcel’s weight and dimensions are combined to calculate the rate and available services and the origin zip code and destination zip code and corresponding USPS Zone also determine the final label fee.

What is the cheapest way to ship with USPS?

Whether you are shipping a letter weighing less than one ounce, a large envelope weighing up to 13 ounces, or a package weighing up to 16 ounces, First Class mail is the most affordable shipping option available.

If you want to get great discounts on these services as well as USPS Media Mail, Priority Mail, Parcel Select, and more, sign up for a ShipStation trial now and start saving time and money on your shipping.

Start Saving on postage by trying ShipStation for free for 30 days!