Key points:

  • USPS shipping rates are primarily based on the dimensions, weight and contents of a package, plus the end customer's destination and required delivery speed
  • USPS offers a wide range of domestic and international shipping solutions, all with different features and pricing to fit almost every eCommerce store
  • Easyship can help you instantly save up to 89% off the retail price of USPS rates, without any need for complicated calculations

Looking at how to calculate shipping costs for USPS? From dimensional weight to surcharges and price tiers to taxes, this article breaks down how USPS calculates shipping costs. Plus, explore the different delivery options available and how Easyship can help you effortlessly find the cheapest USPS rates.

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How Are USPS Shipping Rates Calculated

Shipping costs are calculated by a range of factors, each one unique for each shipment. While some are obvious, others you may not have thought of and can quickly add to the price of shipping orders to customers. Checkout the quick breakdown below to make sure your shipping strategy is sustainable for all sales:

Dimensional Weight

Most carriers use the volume weight of a package as a key factor to calculate an accurate shipping price, because it takes into account both size and weight. This measure determines both a package's weight and how much space it will take up, as opposed to just the weight of a package driving up cost. In some cases, smaller and heavier packages can work out cheaper than larger and lighter.

While USPS may not ask for the volume weight directly, when you input figures such as the combined length and girth of a package, plus the weight, the dimensional (DIM) weight will be calculated by the courier. USPS only applies DIM weight pricing to packages over one cubic foot for Priority Mail Express, Priority mail and Parcel Select USPS services.

To calculate whether this shipping cost will apply to your packages yourself, follow the formula below:

  1. The first step is calculating whether your package is more than 1 cubic foot or 1,728 cubic inches. To calculate this, multiply the length, width and height (L x W x H) and if this total is under 1,728, then DIM pricing may not apply.
  2. If the total is above 1,728, then check the physical weight of your package
  3. Calculate the DIM weight using the USPS formula: L x W x H/166. If the total of this calculation is higher than the total weight figure, you will pay the DIM price.

Shipping Price Tiers

There are different pricing tiers for the different types of customers looking to ship with USPS. eCommerce entrepreneurs can save money on shipping services by making sure their orders are being delivered with the correct pricing tier. Checkout this quick summary below

  • Post Office Rates. Most retail customers use these USPS postage rates, and they are generally quite expensive. This starting tier for pricing is what you would pay at the local post office for a one-off shipment
  • Commercial Pricing. These are more affordable rates for high volume shippers, offering discounted rates to busy businesses. With Easyship, these rates are available for all customers, with no minimum volume.

Until January 2023, USPS previously offered Commercial Base Pricing and Commercial Plus Pricing. These have now been merged into a single commercial pricing category.


For certain types of USPS post, the further the distance a package travels, the greater the price. These distances are worked out using different zones, with zone 1 being local to your area, while zone 9 a distant location. The more zones your package goes through, the more the postage cost.

The following services are not zoned, and you pay the same no matter the destination zip code:

  • First-Class Mail
  • USPS Marketing Mail
  • Library Mail
  • Media Mail

While the following services are all zoned and your costs will increase the more zones your order crosses:

  • Priority Mail Express
  • Priority Mail
  • USPS Retail Ground
  • Bound Printed Matter

USPS also offers domestic Priority Mail Express and Priority Mail Flat Rate services for packages sent in USPS branded Flat Rate packaging. This covers parcels up to 70lbs and to any destination. For Flat Rate international services to any destination country, you can use the same flat rate boxes packaging for Priority Mail Express International or Priority Mail International.

Duties and Taxes

If you are shipping to international customers, taxes can make a simple order from your store into a complex delivery. You must fill out customs forms for USPS services, except for First-Class Mail International envelopes under 15.994 oz.

Each destination country will have its own specific requirements and different potential costs. With over 220 countries in the world, checking the requirements for each one can take a long time for a busy store. Easyship's free duties and taxes calculator can instantly find estimates for your frequent shipping destinations, simplifying customs clearance.


Surcharges are extra costs that are added to the base rate offered by the courier. As they can significantly increase the cost of shipping, it can be important to be aware how these are determined. In general, anything that could make your package fall outside of general shipping rules can impact the price. These are some common reasons:

  • Fuel surcharge
  • Packages that are greater than carrier's format
  • Delivering to remote locations
  • Updating address
  • Dangerous goods

Related post: What's the Cheapest Way to Ship Packages?


Classes of Mail

The USPS breaks down all of their different services into options labelled classes. Each class package will have its own different prices, features, requirements, speeds and service levels. For most packages, the contents, destination and required speed will determine which class of mail you will pick.

USPS Domestic Services

With a huge network connecting every corner of the country, USPS is a top domestic shipping solution for many online businesses. For a quick run down of the services available, plus how much you can save with Easyship, checkout the breakdown below:

  1. First Class Mail. Get orders under one pound delivered in 1-3 business days, plus tracking updates.
  2. First Class Signature. For lightweight shipments like the above option, however, this service also offers signature updates.
  3. Priority Mail. While delivery time is also 1-3 business days and tracking is also available, you can ship larger parcels up to 70 lbs.
  4. Priority Mail Signature. Similar to Priority Mail, however, orders shipped with this option will only be released to the end customer once the package is signed for.
  5. Priority Mail Express. The fastest delivery service available from this courier, with a one-day tracked overnight delivery to urban areas and a two-day overnight delivery to rural areas.
  6. Priority Mail Flat Rate. The most affordable way to ship bulkier, heavy items over distances. Packages under 70lbs will pay a fixed fee determined by the size.
  7. Priority Mail Express Flat Rate. This faster delivery for flat rate packages is available for all packages under 70lbs.

USPS International Services

USPS has international shipping options to a wide range of destinations. Pick the service that works best for your needs based on delivery speed, features like tracking and insurance.

  1. USPS First Class International. One of the most affordable international shipping options for items under 4lbs. This service includes tracking and delivery in 1–4 weeks.
  2. USPS Priority Mail International. This faster premium delivery service is for packages weighing under 1lb and delivery takes between 6-10 business days.
  3. USPS Priority Mail Express International. The fastest delivery for international shipments over 1lb or more, delivery is expected within a 3-5 business day window.
  4. USPS Flat Rate (International). The most affordable option for large and bulky orders to customers in faraway destinations. This service charges a fixed fee for shipments under 70lbs, with delivery estimated to take 6-10 business days.
  5. USPS Priority Mail Express Flat Rate International. This option is the cheapest way to quickly get packages under 70lbs to a wide range of countries. The delivery timeline is 3-5 business days and includes free tracking.

Find the Cheapest USPS Shipping Rates

Choosing the right carrier is one of the most important aspects of shipping. As one of the most recognizable and trusted shipping solutions in the US and the wider world, USPS can help you ship an order to happy customers almost anywhere.

Low shipping costs can be crucial to the success of an eCommerce store. Start combining USPS's wide range of domestic and international shipping options, with Easyship's powerful shipping tools to access the cheapest USPS rates today.

Free Shipping Rates Calculator: Find the best USPS rates with Easyship. Instantly compare exclusive prenegotiated rates with up to 89% off the retail price, unavailable through the USPS shipping calculator.

Looking for cheap USPS shipping rates? Sign up for an Easyship account today and effortlessly create a fast delivery experience customers love, while also increasing your margin