USPS Priority Mail: Weight Rates vs Flat Rate packages (domestic)

Welcome to the USPS Priority Mail guide to domestic service and package rates.
Learn how to use this guide.

In this guide, we compare specific USPS Priority Mail services: Flat Rate packages versus weight-based rates. To make a comparison using this guide, get an accurate weight of the package you want to ship as well as know the size of the product and packaging it will be shipped in. Use this guide if your packages meet all the following:

  • Weigh less than 70 lbs
  • Dimensions smaller than 13-5/8" x 12" x 5-1/2"

If your packages exceed any of these - compare other Priority Mail options.

Comparing Weight-Based Service and Flat Rate Packaging

When discussing domestic services, both Flat Rate and weight-based packages may weight up to 70 lbs.

Package Size

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.

Package type

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 Flat Rate packaging. With Flat Rate packaging, one rate applies to the package type, regardless of distance (zone) or weight.

Zone

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 general, you'll see that weight-based rates are sometimes better for shipments traveling shorter distances while Flat Rate packages have an advantage for heavier parcels traveling further.

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.

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.

Table Legend

Legend for Comparison Tables
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 Service - vs - all Flat Rate Packaging

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 Service - vs - all Flat Rate Packaging
Commercial Prices by Zone
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

Weight-Based Service - vs - Flat Rate Envelopes (regular and legal)

Flat Rate Envelopes 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 Service - vs - Flat Rate Small Box and Padded Envelope

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 Service - vs - Flat Rate Small Box and Padded Envelope
Commercial Prices by Zone
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

Weight-Based Service - vs - Flat Rate Medium Box

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 Service - vs - Flat Rate Medium Box
Commercial Prices by Zone
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

Weight-Based Service - vs - Flat Rate Large Box

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.

Weight-Based Service - vs - Flat Rate Large Box
Commercial Prices by Zone
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

Continue Comparing Weight-Based Service or Flat Rate Packaging

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 Service

Is weight-based a good fit for your shipments? If so, take a look at these other rate comparison guides:

Start your 30-Day Free Trial with ShippingEasy.

Was this article helpful?
8 out of 37 found this helpful

Comments

Add a Comment

Please sign in to leave a comment.