Welcome to the USPS Priority Mail guide to domestic service and package rates series. Learn how to use this guide.
In this guide, we compare specific USPS Priority Mail services: Flat Rate packages versus weight-based rates. Learn more about USPS Priority Mail.
Overview of service comparison:
When discussing domestic services, both Flat Rate and weight-based packages may weight up to 70 lbs.
Weight-based services offer the most flexibility. Shippers use their own packages with the restriction that package girth not exceed 108" inches. As the name indicates, weight is a factor in determining postage costs.
Zone is also a factor, with rates increasing as the distance (zone) increases. The first 3-digits of your destination ZIP Code determine the zone, which is what is used if you are shipping locally. If you are shipping non-local, the zone is determined by how many zones it crossed to arrive at the destination. You can look up the zone for you shipment using the USPS Zone lookup tool.
In the case of Flat Rate packages, the USPS requires using specially marked boxes. Contents must fit comfortably and packaging must be sealed without any bulging. Learn more about USPS Regional Rate packaging. With Flat Rate packaging, one rate applies to the package type, regardless of distance (zone) or weight.
Detailed service comparison:
The tables below provide a visual summary of when it's best to use a Flat Rate box or a custom package with weight-based service, based on weight and zone:
- Weight vs All Flat Rate packaging
- Weight vs Flat Rate Envelopes (regular and legal)
- Weight vs Flat Rate Small Box and Padded Envelope
- Weight vs Flat Rate Medium Box
- Weight vs Flat Rate Large Box
TIP: to simplify the data, we use a color and letter code to indicate the best packaging. Please keep in mind that services listed are only the best value when your products will fit into the defined package dimensions. Use the legend below to read the following charts.
Legend for comparison tables |
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| Priority Mail Service | Code | Packaging |
| Flat Rate | E | Regular Envelope Legal Envelope |
| S | Small Box All Envelopes |
|
| M | Medium or Small Boxes All Envelopes |
|
| L | All Boxes or Envelopes | |
| Weight-based | W | Any package less than 108" girth |
Weight-based rates versus all Flat Rate packaging:
Weight-based rates vs all Flat Rate packagingPrices by Zone: Commercial Plus |
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| Weight Not Over (Lbs) |
Zones 1 & 2 Local |
Zone 3 | Zone 4 | Zone 5 | Zone 6 | Zone 7 | Zone 8 | Zone 9 |
| 0.5 | E | E | E | S | S | S | S | S |
| 1 | E | E | E | S | S | S | S | S |
| 2 | E | S | S | S | S | S | S | M |
| 3 | S | S | S | S | S | M | M | L |
| 4 | S | S | S | S | M | M | L | L |
| 5 | S | S | S | S | M | L | L | L |
| 6 | S | S | S | M | L | L | L | L |
| 7 | S | S | S | M | L | L | L | L |
| 8 | S | S | S | M | L | L | L | L |
| 9 | S | S | S | M | L | L | L | L |
| 10 | S | S | S | M | L | L | L | L |
| 11 | S | S | S | M | L | L | L | L |
| 12 | S | S | S | L | L | L | L | L |
| 13 | S | S | S | L | L | L | L | L |
| 14 | S | S | S | L | L | L | L | L |
| 15 | S | S | S | L | L | L | L | L |
| 16 | S | S | S | L | L | L | L | L |
| 17 | S | S | S | L | L | L | L | L |
| 18 | S | S | S | L | L | L | L | L |
| 19 | S | S | M | L | L | L | L | L |
| 20 | S | M | M | L | L | L | L | L |
| 21 | S | M | M | L | L | L | L | L |
| 22 | M | M | M | L | L | L | L | L |
| 23 | M | M | L | L | L | L | L | L |
| 24 | M | L | L | L | L | L | L | L |
| 25 and up |
L | L | L | L | L | L | L | L |
Take away:
Overall, Flat Rate packaging provides a better value than weight-based pricing. However, this only applies if your products fit within the defined dimensions of the Flat Rate packages.
Compared with weight-based rates, Flat Rate Envelopes and Small Boxes have a distinct advantage when shipping shorter distances, Zones 1-4, and for parcels weighing less than 20 lbs. These packages are also the best across zones for very light shipments, weighing less than 2 lbs.
Flat Rate Medium and Large Boxes offer a better value over weight-based rates for shipments traveling further, Zones 5-9. They are also more competitive, across zones, for packages weighing more than 20 lbs.
In any instance where a Flat Rate Medium or Large Box is a better value than weight-based rates, you would see even greater savings when using a Small Box or Envelope.
Weight-based rates versus Flat Rate Envelopes (regular and legal):
These offer the least expensive USPS Priority Mail rate around. If you ship flat items that fit in these envelopes, it's your best option. Learn how to assign a carrier service to shipments containing specific products.
Weight-based rates versus Flat Rate Small Box and Padded Envelope:
Weight-based rates vs Flat Rate Small Box and Padded EnvelopePrices by Zone: Commercial Plus |
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| Weight Not Over (Lbs) |
Zones 1 & 2 Local |
Zone 3 | Zone 4 | Zone 5 | Zone 6 | Zone 7 | Zone 8 | Zone 9 |
| 0.5 | W | W | W | S | S | S | S | S |
| 1 | W | W | W | S | S | S | S | S |
| 2 | W | S | S | S | S | S | S | S |
| 3 | S | S | S | S | S | S | S | S |
| 4 | S | S | S | S | S | S | S | S |
| 5 and up |
S | S | S | S | S | S | S | S |
Take away:
If your products fit into a Flat Rate Small Box or Padded Envelope, you should generally use these services over a custom package. With an exception, very light-packages traveling a very-short distance, Zones 1-4, may get a better price with weight-based rates. Consider the cost of buying your own packaging against any savings in postage.
Learn how to assign a carrier service to shipments containing specific products.
Weight-based rates versus Flat Rate Medium Box:
Weight-based rates vs Flat Rate Medium BoxPrices by Zone: Commercial Plus |
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| Weight Not Over (Lbs) |
Zones 1 & 2 Local |
Zone 3 | Zone 4 | Zone 5 | Zone 6 | Zone 7 | Zone 8 | Zone 9 |
| 0.5 | W | W | W | W | W | W | W | W |
| 1 | W | W | W | W | W | W | W | W |
| 2 | W | W | W | W | W | W | W | M |
| 3 | W | W | W | W | W | M | M | M |
| 4 | W | W | W | W | M | M | M | M |
| 5 | W | W | W | W | M | M | M | M |
| 6 | W | W | W | M | M | M | M | M |
| 7 | W | W | W | M | M | M | M | M |
| 8 | W | W | W | M | M | M | M | M |
| 9 | W | W | W | M | M | M | M | M |
| 10 | W | W | W | M | M | M | M | M |
| 11 | W | W | W | M | M | M | M | M |
| 12 | W | W | W | M | M | M | M | M |
| 13 | W | W | W | M | M | M | M | M |
| 14 | W | W | W | M | M | M | M | M |
| 15 | W | W | W | M | M | M | M | M |
| 16 | W | W | W | M | M | M | M | M |
| 17 | W | W | W | M | M | M | M | M |
| 18 | W | W | W | M | M | M | M | M |
| 19 | W | W | M | M | M | M | M | M |
| 20 | W | M | M | M | M | M | M | M |
| 21 | W | M | M | M | M | M | M | M |
| 22 | M | M | M | M | M | M | M | M |
| 23 | M | M | M | M | M | M | M | M |
| 24 | M | M | M | M | M | M | M | M |
| 25 and up |
M | M | M | M | M | M | M | M |
Take away:
If your products fit into the Flat Rate Medium Box, base your service decision on zone and weight.
For shipments traveling shorter distances, Zones 1-4, and weighing less than 20 lbs, using your own packaging for weight-based rates may be a better value.
Across all zones, though, shipments weighing over 20 lbs will ship for less in a Flat Rate Medium Box.
Likewise, shipments traveling somewhat further, Zone 5, and weighing more than 5 lbs should be considered for the Flat Rate Medium Box. The same holds true for parcels more than 2 lbs traveling even further, Zones 6-9.
Learn how to assign a carrier service to shipments containing specific products.
Weight-based rates versus Flat Rate Large Box:
Weight-based rates vs Flat Rate Large BoxPrices by Zone: Commercial Plus |
||||||||
| Weight Not Over (Lbs) |
Zones 1 & 2 Local |
Zone 3 | Zone 4 | Zone 5 | Zone 6 | Zone 7 | Zone 8 | Zone 9 |
| 0.5 | W | W | W | W | W | W | W | W |
| 1 | W | W | W | W | W | W | W | W |
| 2 | W | W | W | W | W | W | W | W |
| 3 | W | W | W | W | W | W | W | L |
| 4 | W | W | W | W | W | W | L | L |
| 5 | W | W | W | W | W | L | L | L |
| 6 | W | W | W | W | L | L | L | L |
| 7 | W | W | W | W | L | L | L | L |
| 8 | W | W | W | W | L | L | L | L |
| 9 | W | W | W | W | L | L | L | L |
| 10 | W | W | W | W | L | L | L | L |
| 11 | W | W | W | W | L | L | L | L |
| 12 | W | W | W | L | L | L | L | L |
| 13 | W | W | W | L | L | L | L | L |
| 14 | W | W | W | L | L | L | L | L |
| 15 | W | W | W | L | L | L | L | L |
| 16 | W | W | W | L | L | L | L | L |
| 17 | W | W | W | L | L | L | L | L |
| 18 | W | W | W | L | L | L | L | L |
| 19 | W | W | W | L | L | L | L | L |
| 20 | W | W | W | L | L | L | L | L |
| 21 | W | W | W | L | L | L | L | L |
| 22 | W | W | W | L | L | L | L | L |
| 23 | W | W | L | L | L | L | L | L |
| 24 | W | L | L | L | L | L | L | L |
| 25 and up |
L | L | L | L | L | L | L | L |
Take away:
If your products fit into the Flat Rate Large Box, base your service decision on zone and weight.
For shipments traveling shorter distances, Zones 1-4, and weighing less than 25 lbs, using your own packaging for weight-based rates may be a better value.
Across all zones, though, shipments weighing over 25 lbs will ship for less in a Flat Rate Large Box.
Likewise, shipments traveling somewhat further, Zone 5, and weighing more than 12 lbs should be considered for the Flat Rate Large Box. The same holds true for parcels more than 5 lbs traveling even further, Zones 6-9.
Learn how to assign a carrier service to shipments containing specific products.
Continue comparing services:
Consider the conclusions that you've drawn about your shipments and whether or not Flat Rate packages or weight-based rates are the better value. Then use this information to continuing comparing the best of the two with your other Priority Mail service options:
Flat Rate:
Is Flat Rate a good fit for your shipments? If so, take a look at these other rate comparison guides:
Weight-based rates:
Is weight-based a good fit for your shipments? If so, take a look at these other rate comparison guides:
Related articles:
Best of Rules: Assign a carrier service to shipments containing specific products
Best of Rules: Assign a package and dimensions to my shipments
USPS Priority Mail: Guide to domestic service and package rates
Package Sizes and Dimensions: USPS Domestic
ShippingEasy's USPS Rate Tables
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