USPS Flat Rate Shipping Guide: Boxes, Envelopes and Pricing

SendTech Staff Pitney Bowes
09/19/2023 Office

Introduction: Why USPS flat rate shipping is essential for ecommerce businesses

Shipping is a critical part of any ecommerce business strategy. Managing shipping costs, juggling multiple carriers, and staying on top of logistics can be overwhelming—especially when shipping high volumes, heavy items, or bulky products. These shipping costs can pile up quickly, eating into profit margins and complicating operations. 

That’s where USPS flat rate shipping becomes a smart option. With predictable pricing based on package size—not weight or distance—it offers ecommerce businesses a simple and cost-effective shipping solution. No surprises, no calculations, just one flat fee for anywhere in the U.S. 

In this guide, we’ll walk you through everything you need to know about USPS flat rate shipping, including: 

  • The different types of flat rate boxes and envelopes 
  • Pricing, speeds, and best-use scenarios 
  • How to maximize savings and streamline fulfillment 

Let’s dive in and simplify your shipping strategy. 

Table of contents

What is flat rate shipping?

USPS flat rate shipping® is a service that allows businesses to ship packages at a fixed rate, regardless of the package's weight (up to 70 lbs) or destination—so long as it fits within an approved USPS flat rate box or envelope. 

This simplicity is what makes it a go-to for many ecommerce businesses. Instead of dealing with fluctuating shipping prices, zone charts, or weight-based rates, businesses can simply pick the right-sized box or envelope and pay one flat fee. No weighing. No measuring. Just ship. 

Why it’s important for ecommerce businesses

USPS Priority Flat Rate is a favorite among ecommerce businesses because of its simplicity, speed, and cost certainty. There's no need to calculate zones or weigh packages—just pick a size, pack it up, and ship. 

  • Predictable shipping costs: Know what you’re paying upfront. 
  • No surprises: No need to weigh or measure. 
  • Faster fulfillment: Easier planning leads to quicker shipments. 

Whether you're shipping across town or across the country, flat rate keeps the pricing consistent and the process painless. 

Benefits of USPS flat rate shipping for ecommerce businesses

Simplified and streamlined shipping process

Flat rate shipping® removes the need for constant weighing, measuring, and price checking. Just select the right size flat rate box or envelope, pack your products, and send them off. With free package pickup, businesses can avoid unnecessary trips to the post office, making the shipping process more efficient. 

Cost savings and predictable pricing

USPS Flat Rate Shipping® eliminates hidden costs like fuel surcharges, weekend delivery fees, and residential delivery charges. The service offers free packaging and built-in shipping insurance up to $100, providing added value and cost savings. Thanks to flat rate pricing, there are no unexpected fees, making it a reliable solution that ensures predictable shipping costs, helping businesses manage their budgets effectively. 

Fast and reliable delivery

USPS Priority Mail® flat rate delivers packages in 1 to 3 days, while Priority Mail Express® offers overnight shipping with a money-back guarantee. This speed keeps customers happy and supports quick turnaround times. 

Enhanced security and tracking

Each USPS Flat Rate shipment includes USPS free tracking, providing real-time order tracking and offering both businesses and customers peace of mind with constant visibility into the package's transit. In addition to this, USPS ensures secure shipping by placing packages directly in mailboxes, adding extra layer of security. Packages are also safeguarded by law enforcement, minimizing the risk of theft or fraud. USPS also offers re-attempted drop-offs, further enhancing delivery security and ensuring safe, reliable shipments. 

Increased business flexibility and customer satisfaction

USPS Flat rate shipping® is an excellent option for offering free shipping to customers, with predictable shipping costs that make it easy to include shipping fees in product prices. With no extra charges for insurance or packaging, businesses can reduce overhead costs. USPS Flat Rate Shipping allows businesses to ship to virtually anywhere in the U.S.—including Alaska, Hawaii, Puerto Rico, the U.S. Virgin Islands, Guam, as well as Post Office boxes, military bases, and embassies—ensuring extensive flexible shipping options. This extensive reach boosts customer satisfaction and helps businesses manage USPS shipping fees while increasing profit margins. 

How much is flat rate shipping?

USPS Priority Mail® Flat Rate Options offer a range of packaging choices designed for different shipment types. These flat rate boxes and envelopes come with a fixed shipping rate, regardless of weight (up to the limit) or destination, making it easier for eCommerce businesses to manage shipping costs. In this section, we'll explore the available flat rate shipping options, including sizes and prices, to help you select the best packaging for your ecommerce shipping needs. 

USPS flat rate box prices and sizes

USPS provides a variety of Flat Rate boxes in different sizes, each designed to accommodate different types of products. These boxes are perfect for shipping heavier or bulkier items, as the cost remains the same regardless of the weight. This can be especially beneficial for businesses that need to ship items like books, electronics, or home goods. With USPS Flat Rate box prices, companies can better manage shipping costs for their larger items. 

Box type

Size

Best for

Commercial pricing

Price at post office (2025)

Small Flat Rate Box 

8-5/8" x 5-3/8" x 1-5/8" 

Small, dense items like jewelry, books, electronics 

$8.30 

$9.45 

Medium Flat Rate Box 

11" x 8-1/2" x 5-1/2" 

Clothing, shoes, small household goods 

$14.85 

$16.10 

Large Flat Rate Box 

12-1/4" x 12-1/4" x 6" 

Larger or bulkier items, books, apparel 

$20.95 

$22.65 

APO/FPO/DPO flat rate box 

12-1/4" x 12-1/4" x 6" 

For shipping to military addresses (APO/FPO/DPO) 

$20.95 

$22.65 

Large flat rate board game box 

24-1/16″ x 11 7/8″ x 3-1/8″ 

Perfect for shipping board games and other large items 

$22.95 

$24.50 

USPS Flat rate envelope prices and sizes

USPS also offers a range of Flat Rate envelopes, which are compact and designed for lighter or smaller items. These are a great choice for shipping documents, small accessories, and other lightweight products. 

Envelope type

Size

Best for

Commercial pricing

Price at post office (2025)

Flat Rate Envelope 

9-1/2" x 12-1/2" 

Documents, contracts 

$7.75 

$9.25 

Window Flat Rate Envelope 

9-1/2" x 12-1/2" 

Documents or items requiring a visible address window 

$7.75 

$8.25 

Small Flat Rate Envelope 

6-1/8" x 11-1/2" 

Compact documents, small accessories, lightweight items 

$7.45 

$7.95 

Legal Flat Rate Envelope 

9-1/2" x 15" 

Legal-size documents 

$8.05 

$9.65 

Padded Flat Rate Envelope 

9-1/2" x 12-1/2" 

Fragile or padded items 

$8.55 

$10.40 

How much do USPS flat rate boxes and envelopes cost?

Flat rate boxes and envelopes are free to order online or pick up at your local post office. You can even lock in today’s rates with Prepaid Flat Rate Forever packaging®. 

Compared to carriers like FedEx® or UPS®, USPS flat rate shipping offers exceptional value, especially for heavier items. For example, UPS® Simple Rate and FedEx® One Rate may start at higher prices and lack envelope options. 

How USPS flat rate shipping works

Here’s how to ship using USPS flat rate in five easy steps: 

  1. Pick the right packaging: Choose the appropriate USPS Flat Rate box or envelope based on the size and type of items you're shipping, and make sure to measure your items for a comfortable fit. To qualify for the flat rate, you must use USPS packaging, which you can obtain at your local post office or order online from the Postal Store. 
  2. Pack your items: Ensure the package closes flat with no bulging. Verify that the weight does not exceed 70 lbs. 
  3. Label the shipment: Create and print a shipping label via USPS or PitneyShip®. 
  4. Drop off or schedule a pickup: You can give your package to your mail carrier or drop it off at the nearest Post Office for shipment. Alternatively, you can schedule an on-demand pickup for an additional fee. USPS also offers free package pickup, making it more convenient to ship from home. 
  5. Track it: Enjoy free USPS tracking and up to $100 in included insurance. 

It’s important to note that USPS prohibits certain items, such as cigarettes, perfumes, ammunition, and hazardous materials, from being shipped by mail. If you're unsure, refer to the complete list of USPS shipping restrictions. 

When to use USPS flat rate shipping for ecommerce

USPS Flat Rate Shipping is an excellent choice for ecommerce businesses in the following situations: 

  • You're shipping heavy but compact items, as the price is the same regardless of weight. 
  • You send items frequently and want predictable pricing for make budgeting easier. 
  • You prefer to avoid weight-based rate surprises and streamline the shipping However, it may not be the best option when: 
  • Shipping very light packages, as alternatives like First-Class Mail® may be a more cost-effective solution. 
  • You require custom box branding for a more personalized or branded unboxing experience. 

Comparison of USPS flat rate vs. standard shipping

When it comes to choosing between USPS Flat Rate Shipping and Standard Shipping, understanding the strengths of each option is essential for businesses to manage their shipping costs effectively. Flat Rate Shipping is ideal for those who need predictable pricing and are shipping heavier or bulkier items. On the other hand, Standard Shipping is typically better for lighter items or when shipping internationally with carriers like UPS or FedEx. 

Here’s a breakdown of the differences between USPS Flat Rate Shipping and Standard Shipping: 

Feature

Flat rate shipping®

Standard shipping

Pricing

Fixed price regardless of weight or distance 

Prices varies based on weight, size and zone 

Ideal for

Heavy items, nationwide 

Lightweight, local 

Predictability

High 

Variable 

Use flat rate when sending dense, long-distance packages. Standard shipping may offer savings for lightweight or nearby orders. 

Tips for Ecommerce Businesses to Maximize USPS Flat Rate Shipping

To stay competitive and offer customers reliable, cost-effective shipping options, ecommerce businesses can take full advantage of USPS Flat Rate Shipping with these practical tips: 

  • Choose the Right Size Box: Selecting the smallest USPS flat rate box that fits your product is key to maximizing shipping efficiency. By using the appropriate box size, you avoid wasting space and ensure you’re making the best use of available volume, which helps minimize unnecessary costs and maximize the value of your flat rate shipping. 
  • Compare Shipping Options: While Flat Rate Shipping is convenient, it’s still beneficial to occasionally weigh your items. This allows you to compare costs with other options, like First-Class Mail® or Ground Shipping, which may be more cost-effective for lighter items. 
  • Leverage Additional Services: Take advantage of free services included with Flat Rate Shipping, like tracking, insurance, and delivery confirmation. For ecommerce businesses, these features can add value and boost customer satisfaction at no extra cost. Just be sure to check whether you need additional options for specific shipments and if they’re included in your rate. 
  • Stay Ahead of USPS Rate Changes: Shipping costs can change, so it’s crucial to keep an eye on USPS rates and updates to flat rate box sizes. Staying informed allows you to adjust pricing and shipping strategies accordingly, ensuring you continue to offer competitive rates while protecting your profit margins. 
  • Take Advantage of Seasonal Shipping Opportunities: During peak shopping seasons (e.g., Black Friday, Cyber Monday, and the holidays), consider offering promotions with attractive flat rate shipping options. This can help you stand out from the competition, increase sales, and meet customer expectations all while maintaining predictable shipping costs. 

By following these strategies, ecommerce businesses can optimize their use of USPS Flat Rate Shipping, deliver predictable costs, and maintain a competitive edge in the marketplace while providing customers with a reliable shipping experience. 

Maximize savings with USPS flat rate shipping and PitneyShip®

Make the most of every USPS flat rate box by filling it efficiently—since you’re paying for the box size, not the weight. Use flat rate envelopes for lightweight items like documents to keep shipping costs low. Print shipping labels online through USPS or PitneyShip® to access discounted rates and batch label printing. Flat rate is also perfect for subscription boxes or bundled products, and PitneyShip® helps ecommerce businesses track shipments, manage costs, and streamline operations. 

Conclusion: Is USPS flat rate shipping right for your ecommerce business?

If you’re looking for a simple, affordable, and fast shipping solution, USPS flat rate is a smart choice. It takes the guesswork out of shipping costs, supports high delivery reliability, and helps ecommerce businesses of all sizes save time and money. 

Start shipping smarter with USPS flat rate and PitneyShip® today. 

Flat rate shipping FAQs

How long does it take to get flat rate shipping?

USPS Flat Rate Shipping typically uses USPS Priority Mail®, which delivers within 1–3 business days for domestic shipments, depending on the destination. If you need faster delivery, USPS Priority Mail Express® is an expedited option that guarantees delivery overnight or within 1–2 days. 

How do I order USPS flat rate boxes?

You can order USPS Flat Rate boxes for free online on the USPS website or pick them up at your local post office. 

Does USPS flat rate include tracking?

Yes, USPS Flat Rate shipping includes free tracking for all shipments, providing real-time  

What is the weight limit for USPS Flat Rate shipping?

The weight limit for USPS Priority Mail Flat Rate shipping is 70 lbs for all Flat Rate boxes and envelopes, regardless of the weight or destination.