A detailed guide on USPS flat rate boxes

Shipping plays a vital role in your eCommerce. If you do not ship your products at an affordable rate and carefully, your eCommerce reputation is at stake. It would be ideal to reduce the shipping cost, using USPS flat rate shipping. The best part of using USPS flat rate shipping is that if you are sending heavy items, it will save you money. On the other hand, if you are using USPS to send lightweight items, then you are at a loss.

Let us have a deeper understanding of what flat rate shipping is about in this article.

What is flat rate shipping?

In order to improve the customer’s shopping experience and reduce shipping costs [ Compare the Shipping Cost & Estimated Delivery Date from Leading Shipping Carriers ], USPS offers flat rate boxes and envelopes for online stores. The weight of the package is the prime factor that determines the shipping costs, which is ideal for all online stores.

Why is flat rate shipping best for eCommerce?

If you see, flat rate shipping is the most affordable way of shipping, when you consider eCommerce. When you consider shipping costs based on distance or even dimensional weight which is again calculated on the basis of the dimensions like width, height, weight, etc. of the package. Even flat rate shipping works well with certain brands where the shipping cost is inevitable.

Here are some specific features that make USPS flat rate boxes ideal :

  1. Known and fixed prices: On USPS, the shipping box dimensions are fixed and the price too. Hence no surprise costs for your shipping.
  2. Priority delivery: It is important to note that priority packages also get special consideration while delivering.
  3. No surcharges for delivery: USPS Flat rate shipping does not charge you for any shipment.

How does flat rate shipping work?

Note that the flat rate means that the shipping charges are not connected to the shape, weight or size of the shipping item. It also depends on how much stuff you can pack in the flat rate boxes issued by USPS.

In order to ship using flat rate, follow these steps:

  1. Get a flat rate box of required dimensions, that will help you fit in all the necessary items for your customer. There are small, medium and large sizes of boxes at USPS flat rate. The prices are directly proportional to the size of the box. The maximum weight that is allowed is around 70 pounds.
  2. Secondly, pack your items to be delivered and then label the shipping address.
  3. Once done, the box is ready to ship.

Cost of Flat rate shipping boxes

The cost of the flat rate shipping completely depends on the box’s dimensions. The USPS website also gives better detailed data regarding flat rate boxes and their rates.

Flat Rate Service Dimensions At the Post Office
Flat Rate Envelope 12 1/2″ x 9 1/2″ $6.70
Padded Flat Rate Envelope 12 1/2″ x 9 1/2″ $7.25
Legal Flat Rate Envelope 9 1/2″ x 15″ $7.00
Small Flat Rate Box 8 11/16″ x 5 7/16″ x 1 3/4″ $7.20
Top-load Medium Flat Rate Box 11 1/4″ x 8 3/4″ x 6″ $13.65
Side-loading Medium Flat Rate Box 14″ x 12″ x 3 1/2″ $13.65


USPS Flat rate shipping delivery speed

When you consider shipping with USPS, you can find several plans that will help you decide on the shipping priority. There are plans for shipping which deliver overnight or in 1-3 day time or maybe more. USPS has flexible shipping plans for every user.

Why use flat rate shipping for eCommerce?

The best part of adapting USPS for eCommerce shipping is that there are no hidden charges. Hence, lower predictable costs make flat rate shipping ideal for a small-scale eCommerce business.

The few points that make flat-rate noteworthy for eCommerce are:

  1. You need not worry about the weight of your package if it is nothing up to 70pounds.
  2. Each package is insured up to $50.
  3. You can drop off your items at any USPS  store.
  4. Efficient tracking is offered by the USPS itself with its website.

Priority Mail

One of the finest options is to get your package delivered in 1-3 business days based on the package and the location to which it is sent to. The price starts at $7.35 at the Post Office as well as online. It includes free package pickup from the office or home also includes $50 of insurance too. The service also includes no surcharges and no charges for Saturday delivery.

Flat Rate Envelope

Priority Mail || USPS Flat rate boxes

Dimensions :12 1/2″ x 9 1/2″

Price : Commercial Base- $6.95 and Post Office (retail & online) – $7.35

Best used for: Documents, Letters, Manuscripts, passports etc.

Priority Mail  Flat rate envelopes are easy to use and quick. It is perfect to simplify the process of sending and receiving your documents. It uses a proposed flat rate regardless of weight or any particular dimension or even destination and ships in a single envelope (1-5) or a pack of 10.

Gift Card Flat Rate Envelope

priority-mail-gift-card-flat-rate-envelope || USPS flat rate boxes

Dimensions: 10″ x 7″

Price : Commercial Base- $6.95   and Post Office (retail & online) – $7.35

Best used for Oversized Greeting Cards or Gift Cards

Gift Card Flat Rate Envelope is ideal for oversized greeting cards. It is a Priority Mail Flat rate, hence you get assisted domestic services at a low flat rate.

Window Flat Rate Envelope

priority-mail-window-flat-rate-envelope || USPS flat rate boxesDimensions: 10″ x 6″
12 1/2″ x 9 1/2″

Price: Commercial Base –  $6.96  and Post Office (retail & online) – $7.35

Best used for pre-addressed envelopes

Window flat rate envelop is best used for mail that is pre-addressed to the receivers. The letters need to be clearly inserted into the envelope wherein the address needs to be on the window portion of the envelope.

Small Flat Rate Envelope

Small -fat-rate-envelop || USPS Flat rate boxes
Small Flat Rate Envelop: Image Source: USPS

Dimensions: 10″ x 6″

Price: Commercial Base –  $6.95  and Post Office (retail & online) – $7.35

Best used for:  Passports and Small documents.

It mostly allows for a pack of 10 to be shipped. It also allows folded documents. Mostly used for sending letters, cards or even small documents.

Padded Flat Rate Envelope

priority-mail-padded-flat-rate-envelope || USPS Flat rate boxes

Dimensions:  12 1/2″ x 9 1/2″

Price: Commercial Base – $7.55  and Post Office (retail & online) –  $8.00

Best used for: Clothing, Boxed Jewelry, and Books

Get extra protection for your orders with bubble padding on your packages using a padded flat-rate envelope.

Legal Flat Rate Envelope

Legal Flat rate envelop || USPS flat-rate boxes

Dimensions: 15″ x 9 1/2″

Price : Commercial Base-  $7.25  and Post Office (retail & online) – $7.65

Best used for : Legal Document

Perfect when you want to ship legal documents which is important. This can be shipped at a flat-rate. The package contains 10 envelopes for one order.

Small Flat Rate Box

Small Flat-rate boxes || USPS flat-rate boxes

Dimensions:   Outside: 8 11/16″ x 5 7/16″ x 1 3/4″ and Inside: 8 5/8″ x 5 3/8″ x 1 5/8″

Price: Commercial Base – $7.50  and Post Office (retail & online) -$7.90

Best used for small electronics and brochures.

The dimension of the box is equivalent to a stacked set of three DVDs.It is perfect for event tickets, jewelry, electronics, or maybe smaller items. The items packed need expedited shipping and like all other USPS flat rate boxes, it is free. Also feasible for international shipping.

Medium Flat Rate Box – 1(top-loading)

Priority mail medium flat rate box || USPS flat rate boxes


Dimensions: Outside: 11 1/4″ x 8 3/4″ x 6″ ; Inside:  11″ x 8 1/2″ x 5 1/2″

Price: Commercial Base – $12.80  and Post Office (retail & online) – $14.35

Best used for: Shoes or even office supplies.

Irrespective of the size, weight, or destination, a Priority mail medium flat rate box is an easy way to ship products.

Medium Flat Rate Box – 2

Priority mail medium flat rate box || USPS flat rate boxes

Dimensions:  Outside: 14″ x 12″ x 3 1/2″  ; Inside : 13 5/8″ x 11 7/8″ x 3 3/8″

Price : Commercial Base-  $12.80 and Post Office (retail & online) -$14.35

Best used for: Shoes and Office Supplies.

Quick and the most convenient way to ship Priority mail packages which focus on predetermined rates irrespective of weight or destination. This box can also be used for Domestic Priority mail as well as International priority mail. The international priority mail the weight limit of less than 20lbs is mandatory. A single box of it equals 1-5 single boxes

Large Flat Rate Box

Large flat rate boxes || USPS Flat rate boxes

Dimensions:  Outside: 12 1/4″ x 12 1/4″ x 6″ ; Inside: 12″ x 12″ x 5 1/2″

Price : Commercial Base-  $17.60  and Post Office (retail & online) – $19.95

Best used for gift packing, laptops, computers, etc.

Get your orders fulfilled at a quicker pace with larger flat rate boxes. The larger boxes also contain carrier release endorsement, which allows them to leave the box when the receiver is not available.

APO/FPO/DPO Flat Rate Box

priority-mail-apofpo-flat-rate-box || USPS Flat rate box

Dimensions: Outside: 12 1/4″ x 12 1/4″ x 6″ ; Inside: 12″ x 12″ x 5 1/2″

Price: Commercial Base – $16.10  and Post Office (retail & online) – $18.45

Best used for:  Sending gifts  to troops

Ideal for sending gifts to military troops or personnel working overseas, a priority-mail APO FPO flat rate box is used. Mostly the shipping is done within 5-7 days.

Large Flat Rate Board Game Box

Large Flat Rate Board Game Box || USPS Flat rate boxes

Dimensions: Outside: 24 1/16″ x 11 7/8″ x 3 1/8″ ; Inside:  23 11/16″ x 11 3/4″ x 3″

Price: Commercial Base-  $17.60  and Post Office (retail & online) – $19.95

Best used for:  board games

The box ideally fits two average-sized board games. It takes 5-7 days for in-stock items to be delivered.

Prepaid Forever® Priority Mail
Flat Rate® Packaging

Dimensions:  Various dimensions and sizes available

Price :  Post Office (retail & online) – $7.35

Best used for: Various options.

In Prepaid Forever Priority Mail flat rate boxes, several options are available to use.

Priority Mail Regional

It is a better alternative to Priority Mail flat rate boxes for low-cost shipping with a series of choices on the boxes. This is an ideal choice for a better speed of delivery. Regional box costs are calculated on the basis of the zone to which it is transferred and the box size.

Priority Mail Open and Distribute

For your bulk transfer of mailings and products, use priority mail open and distribute. The price is charged based on the regular priority mail distance-based prices, then once the bulk items reach the destination, then it is distributed to the respective recipient. They are not charged based on the weight of the box but on the zone to which it is sent and the size of the tray boxes.

USPS has a varied range of flat-rate boxes that can accommodate your shipping needs. All you need is to meet the mailing standards as prescribed by the United States Postal Service.

Even though USPS has an efficient tracking system, we can also include the tracking system in your WooCommerce store to augment the efficiency of your shipping system. Having an in-house tracking system for every WooCommerce eStore is better to build your brand.

How to integrate flat-rate shipping using ELEX WooCommerce USPS Shipping Plugin with Print Label

Get your eCommerce store easily integrated into your USPS tracking efficiently using ELEX WooCommerce USPS Shipping Plugin with Print Label. This extension will help you to automate your USPS shipping by tracking and displaying the necessary details. The plugin lets you directly take control of your package tracking through USPS without even logging into the USPS website. Here is how the flat rate boxes are enabled for your shipping using the plugin.USPS flat rate services can be chosen based on your eCommerce requirement. Once the order is placed and the shipment is shipped, you will get to track all the necessary details from the USPS shipment tracking screen. According to the tracking setting, you can easily capture the data of your package through live tracking details.


In order to reduce your shipping cost, it is ideal to use a flat-rate shipping method. It is always better to get a clearer picture when you consider shipping-related data. With efficient tracking for USPS, it is the perfect way to get your eCommerce product shipped.

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