The United States Postal Service, known as USPS, is a popular carrier used by e-retailers of all sizes. As an agency of the United States government, it’s a bit unique compared to other shipping carriers, offering a diverse selection of shipping services that are both cost-effective and flexible.

Shipping Methods

USPS offers plenty of shipping methods for delivering orders of all shapes, sizes, and weights.

First Class Mail

USPS’ First Class Mail is legendary for its cost-effectiveness — but only if your shipment is lightweight. First Class deals exclusively with orders weighing less than 15.99 ounces, delivering them within 1 - 3 days at low rates.

When it comes to First Class, the packaging is in your hands. USPS doesn't offer supplies (like they do with other methods), and they have dimensional requirements on such shipments:

ENVELOPES Minimum Size Maximum Size
Height 3.5" 6.125"
Length 5" 11.5"
Thickness 0.007" .25"
Weight 0 15.99 oz
Height 12"
Length 15"
Thickness .75"

Priority Mail

Once your shipment surpasses 15.99 ounces and weighs a pound, it’s time to use USPS’ Priority Mail. With a weight limit of 70 pounds, Priority Mail offers plenty of options for shipping, all in the form of boxes.

Unlike First Class, USPS provides the packaging for Priority Mail shipping, and — best part is — the supplies are all free of charge. If it fits in the box, it ships within one to three days.

Because Priority Mail is a catch-all for all shipments weighing a pound or more, there are a few box choices to choose from.

Priority Mail Flat Rate

The words “Flat Rate” are exactly as they sound. Flat rate essentially means if you ship an order via a USPS Flat Rate box, you get charged a single rate, regardless of where it's going. The smaller the box, the cheaper the rate, and as long as the order fits in the box and weighs less than 70 pounds for boxes and 4 pounds for envelopes, you’re good to go.

Flat Rate Envelope 12.5" x 9.5"
Legal Flat Rate Envelope* 9.5" x 15"
Padded Flat Rate Envelope** 12.5" x 9.5"
Small Flat Rate 8.6875" x 5.4375" x 1.75"
Medium Flat Rate (Top Loading) 11.25" x 8.75" x 6"
Medium Flat Rate (Side Loading) 14" x 12" x 3.5"
Large Flat Rate (Side Loading) 12.25" x 12.25" x 6"
APO/FPO Large Box*** 12.25" x 12.25" x 6"

*A legal envelope is a slightly larger envelope that’s usually used to transport legal documents.

**Padded envelopes are exactly as they sound — envelopes lined with bubble padding that adds an extra layer of protection for more fragile orders.

***APO and FPO options refer to military locations, with the former indicating an Army Post Office and the latter a Fleet Post Office.

Priority Mail Flat Rate also has a hastier option, dubbed Priority Mail Express, that delivers shipments within a day at a flat rate. Packaging dimensions are the same, but only Flat Rate Envelopes, Legal Flat Rate Envelopes, and Padded Flat Rate Envelopes are usable.

Priority Mail Regional Box

Coming in two forms, Box A and Box B, Priority Mail Regional Box is a shipping method available only online. How much you pay for Regional Rate boxes varies based on the distance they’re to be delivered. But like Flat Rate, weight plays a diminished role — the distance, or zone (which we’ll get to later), is what matters most.

The only difference between Regional Rate Box A and B is size and weight limit:

REGIONAL RATE A Dimensions Maximum Weight
Side Loading 11.0625" x 2.5" x 13.0625" 15 lbs
Top Loading 10.125" x 7.125" x 5" 15 lbs
REGIONAL RATE B Dimensions Maximum Weight
Side Loading 14.5" x 3" x 16.25" 20 lbs
Top Loading 12.75" x 10.5" x 5.5" 20 lbs

USPS Retail Ground

Formerly known as Standard Post, USPS Retail is a way of shipping orders weighing up to 70 pounds within 2 to 8 days. Because of that larger window, Retail Ground is cost-effective, but unpredictable. It’s also restricted to retail rates only, so it’s only available over the counter at one of USPS’ facilities.

Mail Media

Like Retail Ground, USPS Mail Media ships orders within 2 to 8 days — but they only ship educational materials. And that can include a range of things:

  • Books
  • Sheet music
  • Scripts
  • Physical records like CDs, DVDs, or cassettes
  • Printed educational materials
  • Binders
  • 16 millimeter or narrower film

You get the idea — if it’s media-related, it may qualify. But USPS is picky about what orders are eligible for mail media. No video games, digital drives, or any advertisements are allowed.

International Options

Like most carriers, USPS offers international options.

Priority Mail Express International
Delivering in three to five business days, Priority Mail Express International is a global version of your domestic Priority Mail Express. It offers both flat-rate pricing — if it fits in the box, it ships — and the usual pricing based on weight or destination.
Global Express Guaranteed
Their quickest and most expensive international option, Global Express Guaranteed ensures global delivery in one to three days.
Priority Mail International
This method is pretty much the spitting image of Express International, but it’s a longer delivery timeframe of six to eight days at a cheaper rate.

Shipping Rates

The total cost to ship will be determined by a few factors — actual weight or dimensional weight of a shipment, the shipping method you’ve selected, the zone it’s headed to, and any additional charges. Let’s dig into each.

Actual Weight

It’s straightforward: how heavy an order is will impact your shipping rate, and the heavier it is, the higher your rate will go. Not much can be done to reduce the weight of your product, but how it’s packaged will matter.

And that’s not just because of heaviness — it’s also because USPS may apply dimensional weighting instead of using an order’s actual weight.

Dimensional Weight

Actual weight is simple; it’s the weight of your order in ounces, pounds, grams, or kilograms. But in some circumstances, USPS will charge your rate based on dimensional weight, a way of finding cubic weight based on dimensions. How it all works:

Dimensional weight calculation = (Length x Width x Height) / 166

That last number — 166 — is known as a volumetric divisor, a number USPS chooses to determine rates. Compared to some of the carriers, USPS doesn’t use dimensional weight too frequently. They only apply it to Priority Mail parcels larger than one cubic foot that are headed to zones 5 - 9, a pretty lengthy distance.

For instance, let’s say you’re shipping through Priority Mail’s Regional Rate Box A (side loading) and your order weighs 3 pounds. Your dimensions will be 11.0625" × 2.5" × 13.0625". Multiply them together, divide by the divisor, and that’s 361 cubic inches, making dimensional weight 2.17, or 2 rounded down.

When the order is shipped out to zones 5 - 9, your rate will not be determined by dimensional weight. Instead it’ll be based on the actual weight: 3 pounds. Why? Because USPS — and other carriers — will charge you based on which of the two is higher.


For all services other than Flat-Rate, distance is determined by the area where an order’s destination is located, called a “zone.”

Get to know what zones are, as nearly all shipping carriers use the term! They’re essentially ranges of distance that echo out from the location an order is shipped from. Whatever zone your destination ends up falling in will be the zone that determines your rate, and the greater the zone, the higher the cost.

For a look at how zones map out around your ship-from location, enter your zipcode into this tool provided by USPS.

Additional Fees

Compared to other carriers, USPS is lax when it comes to fees. But they do offer several additional services to complement their shipping methods. Of course, many will come at additional cost, and some are free of charge depending on shipping method.

Shipping Insurance
With the exception of Priority Mail Express and Priority Mail shipments (free of charge, they include $100 and $50 respectively), you’ll have to pay for shipping insurance. Based on the declared value (the amount you want insured), it’s $2.10 per $100.
Hold For Pickup
For valuable shipments, a pickup can be arranged where customers head to a designated post office to retrieve their packages. It’s completely free.
USPS Tracking
All packages include tracking, which allows you and the customer to keep tabs on an order as it makes its way to its destination.
Special Handling
For fragile items, USPS will handle it with extra care, so long as you’re willing to pay $10.25 per package.
Certificate of Mailing
In the event that there’s a dispute, it’s up to the shipper, not USPS, to offer up evidence that an item was sent. It will cost $1.35 to get a Certificate of Mailing that does exactly that by recording the date USPS received your shipment.
Collect on Delivery (COD)
At $7.15, you can choose to let the customer pay for their purchase and cost to ship at the moment of delivery.
Certified Mail
Take delivery security a step further and receive a receipt as proof that a delivery was attempted or made to the order’s address. If a Return Receipt is purchased (costs $1.45 per delivery), you can also require a signature confirmation from the customer.
Signature Confirmation
To absolutely ensure delivery, you can pay $2.45 per package to require a more specific signature:
  • Restricted Delivery
    Only allow a specified person to receive a shipment. This service is only available to those who purchase Certified Mail, Collect on Delivery, Registered Mail, or Signature Confirmation, at a cost of $8.30, $4.95, $4.95, and $7.40 respectively.
  • Adult Signature Restricted Delivery
    Only allow the release of a shipment if an adult 21 years of age or older signs. Costs $5.90 per shipment.

Price Tiers

The way USPS prices also distinguishes it from other shippers. There are three tiers that determine a USPS rate price — Retail, Commercial Base, and Commercial Plus. The rates for every shipping method we've mentioned fit into one of these three categories based on how you're accessing postage.

Retail Rates
Retail rates are over-the-counter rates; they're what you'd pay if you walked into your nearby USPS post office to ship a package. They tend to be more expensive than other rates.
Commercial Base Rates
Commercial Base rates are discounted and available through USPS postage providers like Endicia and Pitney Bowes. USPS only offers Commercial Base through approved postage providers, and merchants must purchase through them in order to access the rates.
Commercial Plus
The most heavily discounted, Commercial Plus rates are available exclusively to qualified high-volume shippers. Fulfillment warehouses, large retailers, and shipping software providers (such as ourselves) are able to access these rates due to the large number of shipping labels they produce.

Rate Calculator

Given the complexities, coming up with your rates on your own with 100% accuracy is a difficult task. To figure out USPS shipping rates on your own, take a look at their rate calculator.

Or feel free to log into Ordoro, import your orders, and plug in your shipping specifics to find an accurate rate.

Don't have an account? to get set up and access our USPS shipping rates with discounts of up to 67%!