Ready for Peak Season?Download the Ultimate Peak Toolkit Here

BlogRSS Feed


First-Class Package Service vs. Priority Mail: Which To Choose?

by EasyPost
man smiling holding package

Peak season is just around the corner, and as an ecommerce business, shipping concerns will be top-of-mind for the next few months. With so many carrier options available, deciding what will work best for you can be difficult. It’s essential to deliver parcels on time, undamaged, and at the lowest cost possible, and we are here to help you find that sweet spot. We’ll start by breaking down your USPS options.

First-Class Package Service vs. Priority Mail

The United States Postal Service has a long history – the first Postmaster General, Benjamin Franklin, was appointed in 1775 – and they lead the world in mail and package delivery volume each year. Though they didn’t start shipping packages until 1913, USPS shipping volume reached a staggering 7.6 billion packages delivered in 2021. Today, several parcel delivery options are available with USPS, the two most popular being First-Class Package Service and Priority Mail® shipping.

What is USPS First-Class Mail?

First-Class Mail® is the standard USPS delivery service for cards, letter, and large envelopes (also called flats). First-Class Package Service is for items with dimensions larger than flats, but under one pound. It’s fast, reliable, and affordable, and business discounts are available. This short list highlights the unique parameters of First Class Mail:

  • 1 – 5 business days for mail delivery
  • 2 – 5 business days for small package delivery
  • 3.5 oz max for letters
  • 13 oz max for parcels, retail
  • No tracking, but Certified Mail® is an option

Weight, size, and shape will affect pricing, with additional charges for nonmachinable envelopes (square, lumpy, rigid, etc.), large sizes, and weights that exceed the maximum ounces listed above. In addition, businesses may qualify for discounted rates with a few differences in size and weight requirements for retail vs. commercial shipping.

Mail/Package Type
Max Weight
Size Range
Thickness Range
Letters [Retail]
3.5 ounces
3.5” x 5” – 6.125” x 11.5”
0.009” – 0.25”
Postcards [Retail]
0.99 ounces
3.5” x 5” – 6.125” x 11.5”
0.007” – 0.016”
Flats (Large Envelopes) [Retail]
13 ounces
6.125” x 11.5” – 12” x 15”
0.25” – 0.75”
Package (FCPS) [Commercial]
15.99 ounces
No more than 22” x 18” x 15”
0.75” - 15”

Choose First-Class Package Service shipping for smaller parcels that don’t exceed a pound and when delivery dates are more flexible. In addition, high-volume shippers will benefit from commercial prices – which are available to any business that uses EasyPost’s Shipping API.

What is USPS Priority Mail?

The most popular USPS mail service, Priority Mail, has been around since 1968. It’s the best-selling option for good reason – several good reasons, actually:

  • 1 – 3 business days for domestic delivery
  • Free tracking and insurance
  • Free Flat Rate shipping boxes and envelopes
  • 70 lbs and under shipments don’t need to be weighed for Flat Rate

Priority Mail includes the use of Flat Rate packaging free of charge, and those who go this route pay the same price (a flat-rate fee associated with each envelope or box) for packages up to 70 lbs delivered anywhere in the U.S. Those who use their own packaging will pay variable rates based on the weight of the package and how far the package has to travel to be delivered. For this weight- and zone-based pricing, dimensions matter, and they figure into the cost of shipping a package.

Choose Priority Mail shipping for larger packages, faster shipping, and faster delivery dates. Flat Rate shipping is also a great option if your packages are under 70 lbs and the contents fit into the provided packaging.

What is Media Mail?

Media Mail® is available when you need to ship media and educational materials such as books, films, printed music, video and sound recordings, etc. And as long as the package does not need to be delivered quickly, using Media Mail is more cost-effective than either First-Class Package Service or Priority Mail.

  • 2 - 8 business days for delivery
  • 70 lbs maximum weight

Choose Media Mail to ship media and educational materials if you’re not in a hurry to get the parcel delivered quickly.

Maximum size and weight for USPS packages

When deciding between First-Class Package Service and Priority Mail shipping, one thing to keep in mind is the maximum size and weight restrictions you’ll need to comply with. Though the dimensions are very similar, the weight restrictions are quite different. And for Priority Mail Flat Rate packages, the box size is tied to the rate. So if you need one of the larger boxes, you’ll be paying more.

First-Class Package Service vs. Priority Mail
Restriction Type
First-Class Package Service
Priority Mail
Up to 108” length + girth AND No more than 22” x 18” x 15”
Up to 108” length + girth
Up to 15.99 oz
Up to 70 lbs

Shipping shoes vs. shipping t-shirts

Using an example will highlight the advantages of different shipping options in varying circumstances. To illustrate, we will compare the price and delivery times of shipping a pair of shoes vs. a t-shirt. For this example, we will keep the distance the same and ship from San Francisco, CA, to Austin, TX.

Sneakers vs. T-Shirt
Air Jordan 3
18.6 oz
6 oz
Size Constraints
13.25” x 8.5” x 5”
First-Class Package Service
N/A - too heavy
Expected Delivery
4 – 5 business days
Priority Mail
Priority Mail Flat Rate
$21.50 (large box)
$9.45 (small box)
Expected Delivery
3 business days
3 business days

For the shoes, First-Class Package Service shipping is not an option because the shoes exceed weight limits. Priority Mail is the only option, and because of the Air Jordan shoe box size, the Priority Mail Flat doesn’t make sense at $21.50. It’s much better to save nearly $6 and package it up yourself.

For the t-shirt, First-Class Package Service delivery may be the way to go unless you’re in a hurry. At $5.40 and 4 business days, you’re saving $4.05 and getting it there in only one more day. If you need it delivered quickly, the least expensive option would be to go with Priority Mail Flat Rate shipping. The t-shirt will easily fit into the free small box for a total of $9.45 – and you will save on packaging.

Shipping with EasyPost

We’ve packed a lot of information into this post; luckily, you don’t need to memorize it. Our Shipping API makes it simple to find the fastest, most cost-effective shipping opportunities for your business.

Integrating the free API puts the most reliable technology platform to work for you:

  • Experience 99.99% uptime
  • Save up to 74% on shipping costs
  • Improve on-time delivery to 90% or better
  • Print your own labels
  • Verify addresses
  • Insure your packages
  • Neutralize your carbon footprint
  • Track all your packages
  • Gain access to PC Postage with USPS
  • And more!

Remove the technical complexities of shipping logistics – especially with peak season on the horizon – so you can focus on helping your business grow.

Which should you choose? First-Class Package Service vs. Priority Mail

When choosing between USPS First-Class Package Service and Priority Mail shipping, you’ll want to keep a few things in mind: package size and weight, delivery speed, shipping distance, and cost. Package size, weight, and shipping distance can impact the cost, so you’ll also need to prioritize delivery speed or shipping costs.

First-Class Package Service vs. Priority Mail
Restriction Type
First-Class Package Service
Priority Mail
2 – 5 business days
1 – 3 business days
No more than 22” x 18” x 15”
Up to 108” length + girth
Up to 15.99 oz
Up to 70 lbs
No tracking through USPS
Tracking through USPS
Purchase up to $5k insurance on merchandise
Up to $100 insurance free with most shipments
Shipping Materials
Use your own
Use Flat Rate boxes and envelopes free OR Use your own

So which service wins: First-Class Package Service or Priority Mail? It depends.

Choose First-Class Package Service shipping when you’re shipping items that weigh less than a pound and if you don’t need to get it there within three days. Make sure you take advantage of commercial prices for First-Class Package Service shipping if you go this route to have a bit more flexibility on weight limits.

Choose Priority Mail shipping when you’re shipping heavier items or when you need to get it there in three days or faster. Flat Rate shipping is also a great option that fits well for many ecommerce businesses, plus you’ll save a bit by using free USPS shipping boxes.

If it’s still too much to think about – it is a lot of moving parts – save yourself the headache and use our Shipping API. It will automatically calculate your best shipping option as well as any discounts you’re eligible for. Sign up free today or schedule a time to speak with one of our shipping experts for more information!