Ecommerce Shipping BlogCarrier RatesUSPS Flat Rate vs USPS Priority Mail: Flat Rate Boxes, Prices, and Services

USPS Flat Rate vs USPS Priority Mail: Flat Rate Boxes, Prices, and Services

Posted on July 2, 2022 by

USPS Flat Rate is a commonly used shipping service. A major reason this shipping method is used so frequently is that it’s a very easy parcel size for the USPS to fit into their trucks. It’s also a good way for the USPS to make money. As a result, they’ll usually suggest it when you go into a post office. This is for a couple of reasons: These parcels rarely hit the weight limit and the profit margins on Flat Rate is higher than standard Priority Mail. So, while the USPS loves customers to use Flat Rate packaging, there are times when it’s not as beneficial to merchants and customers. Knowing when Flat Rate options offer the best shipping rate and when standard shipping or Regional Rate boxes offer the best rate is important.

How Does Flat Rate Work?

USPS Flat Rate is a type of USPS Priority Mail® packaging that has specific-sized boxes and envelopes. They can be shipped at one flat fee across the US or to approved international locations—as long as the parcel weighs under 70 lbs. This is good for estimating shipping costs.

When Can I Not Use Flat Rate?

USPS Flat Rate packging CANNOT be used with standard Priority Mail services, First Class Mail, or Media Mail. They are only allowed for their designated Flat Rate service. You can expect a billing adjustment if flat rate packaging is used with an unapproved service.

How much does USPS Flat Rate packaging cost? 

Priority Flat Rate is the USPS’s one-size-fits-all packaging that lets you fit as much as you can into the box as long as it’s under 70 lbs. The prices for Priority Mail Flat Rate and dimensions of each package type are listed below. 

Flat Rate Envelopes 12-1/2″ x 9-1/2″ or smaller$7.40
Legal Flat Rate Envelope$7.70
Padded Flat Rate Envelope$8.00
Small Flat Rate Box$7.90
Medium Flat Rate Boxes$13.75
Large Flat Rate Box$19.30
APO/FPO/DPO Large FRB$17.80

What are USPS Regional Rate Boxes? 

Regional rate boxes function similarly to USPS Flat Rate packaging. However, they do increase in price based on the destination zone. As a result, the closer USPS shipping zones are more affordable than flat-rate packaging. Unlike other Priority Mail services, though, Regional Rate Boxes have weight limits of 15 lbs or 20 lbs. The USPS also doesn’t always push these as hard as they do standard Flat Rate packaging, and there can be additional fees if you purchase the regional rate boxes from the USPS directly. Because of this, it is advisable to use your own label-creation software like ShipStation.

Regional Rate BoxZones
L, 1 & 2
Box A*$7.83$8.04$8.34$9.01$10.89$11.63$12.64$23.37
Box Bº$8.23$8.64$9.56$12.36$17.50$20.10$22.90$42.98

*Max weight 15 lbs.
Side-loading: 11 1/16” x 2 ½” x 13 1/16”
Top-loading: 10 ⅛″ × 7 ⅛″ × 5″
°Max weight 20 lbs
Side-loading: 14 ½″ × 3″ × 16 ¼″
Top-loading: 12 ¼″ × 10 1⁄2″ × 5 ½″

Priority Package Standard Services

Priority Package is the standard parcels for the USPS that weigh under 70 lbs and do not exceed 108″ in combined length and girth (girth = the distance around its thickest part). These parcels will reach their final delivery in the same timeframe as the flat rate and regional rate boxes. However, their prices are structured differently. Whereas flat rate and regional rate don’t have weight factored into them. Each new pound increases the rate for standard Priority Package. This also includes Priority Thick Envelope.

USPS Priority Mail Requirements

  • Maximum weight is 70 lbs.
  • Maximum combined length and girth (girth is the distance around the thickest part) is 108″.
  • For more information on USPS pricing available in ShipStation, click here.
Weight < lbZones L, 1 & 23456789
1 lb$7.16$7.46$7.67$7.88$8.34$8.52$8.80$14.25
2 lbs$7.79$7.96$8.24$8.85$10.44$11.01$11.69$21.81
3 lbs$8.00$8.35$8.72$9.64$12.70$14.10$16.45$29.59
4 lbs$8.10$8.58$9.21$10.43$14.80$16.78$18.96$35.63
5 lbs$8.20$8.63$9.53$11.70$16.87$19.29$21.96$41.46
6 lbs$8.31$8.67$9.64$14.32$19.39$22.52$25.75$47.51
7 lbs$8.73$10.08$10.13$16.53$21.48$25.39$28.93$53.35
8 lbs$8.79$10.58$11.95$18.04$23.59$27.96$32.49$59.89
9 lbs$9.65$10.98$12.45$19.34$25.67$30.28$36.12$66.60
10 lbs$10.15$11.54$12.65$21.11$28.00$33.63$39.67$72.43
11 lbs$12.15$14.54$15.59$24.26$32.07$39.05$45.84$79.13
12 lbs$12.90$15.47$18.16$25.99$34.99$42.24$49.20$84.83
13 lbs$13.57$16.36$19.01$27.38$37.55$43.95$50.94$87.86
14 lbs$14.27$17.26$20.02$28.98$39.67$46.40$53.47$92.21
15 lbs$14.82$18.17$20.99$30.47$41.20$47.29$54.87$94.65

How Can I Get Free USPS Boxes?

Yes! An added bonus of USPS Flat Rate and Regional Rate boxes is that USPS offers free packaging for these services. For Priority Mail Package and Thick Envelope, you usually have to provide your own packaging. Keep in mind, though, that you can only use this packaging for their associated service. If you try and use a Flat Rate box with a standard Priority service or First Class Mail, you should expect a post-billing correction to be made.


For most parcels under about 10 lbs, USPS Priority Mail will be the best option for shipping. If it is going to a faraway destination like Hawaii or opposite coasts, or you’re shipping something heavy, Priority Flat Rate can be more cost-effective. For shipments not going as far, using Priority Mail Package or Regional Rate Boxes can be the most affordable option.

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