Priority Mail Flat Rate: What It Is & When to Use It in 2025
USPS Priority Mail Flat Rate is one of the most popular shipping options for individuals and small businesses in the United States. Its value lies in simplicity and predictability: you pay a fixed rate to ship anything that fits into a USPS-provided flat rate box or envelope—regardless of how much it weighs or how far it travels within the U.S.
In this guide, we’ll explain what Priority Mail Flat Rate is, when it makes sense to use it, and how to choose the right packaging for your needs.
What Is USPS Priority Mail Flat Rate?
Priority Mail Flat Rate is a shipping service offered by the United States Postal Service (USPS) that lets you ship packages up to 70 pounds anywhere in the U.S. for one fixed price, depending only on the size of the box or envelope, not the weight or distance.
This service includes:
- 1–3 business day delivery (depending on origin/destination)
- USPS Tracking
- Up to $100 of insurance
- Free flat rate packaging
- No need to calculate zones or distance-based pricing
Flat Rate shipping is a part of the broader USPS Priority Mail service, but unlike weight-based Priority Mail, your shipping cost is determined by the type of flat rate box or envelope you choose.
2025 Flat Rate Pricing & Packaging Options
Below are the current USPS Priority Mail Flat Rate retail prices for 2025:
| Package Type | Dimensions (approx.) | Retail Price |
|---|---|---|
| Flat Rate Envelope | 12.5″ x 9.5″ | $11.00 |
| Legal Flat Rate Envelope | 15″ x 9.5″ | $11.20 |
| Padded Flat Rate Envelope | 12.5″ x 9.5″ (padded) | $11.95 |
| Small Flat Rate Box | 8.7″ x 5.4″ x 1.6″ | $11.70 |
| Medium Flat Rate Box 1 | 11″ x 8.5″ x 5.5″ | $21.05 |
| Medium Flat Rate Box 2 | 13.6″ x 11.9″ x 3.4″ | $21.05 |
| Large Flat Rate Box | 12.25″ x 12.25″ x 6″ | $29.95 |
Note: Commercial pricing (through online postage services or USPS business accounts) can offer discounts of up to 10–20% per shipment.
When Should You Use Flat Rate Shipping?
Flat Rate shipping is ideal when:
- Your package is heavy for its size (closer to 70 lbs)
- You’re shipping to a far destination or remote zone
- You want to simplify pricing for your customers
- You need fast delivery with built-in tracking and insurance
Real-World Examples:
- A 12 lb box of books from New York to California
- A dense item like tools or electronics shipped long-distance
- A return shipment where a predictable cost saves time and dispute
Flat Rate vs. Weight-Based vs. Cubic Pricing
| Feature | Flat Rate | Weight-Based Priority | Priority Mail Cubic |
|---|---|---|---|
| Pricing Basis | Box size only | Weight + zone | Box size (volume) + zone |
| Max Weight | 70 lbs | 70 lbs | 20 lbs (for best value) |
| Best Use Case | Heavy small items, distance | Lightweight nearby | Small heavy items |
| Box Provided | Yes (USPS-branded only) | No | No |
| Custom Packaging? | No | Yes | Yes |
Tip: If your item is small and dense (e.g. coffee mugs, auto parts), compare Cubic Pricing rates using tools like Pirate Ship.
Pros and Cons of Priority Mail Flat Rate
✅ Pros
- No scale or zone calculators needed
- Predictable, transparent costs
- Boxes and envelopes are free from USPS
- Insurance and tracking included
- Fast shipping (1–3 days)
❌ Cons
- Not ideal for lightweight or bulky items
- Requires USPS-branded flat rate packaging
- Slightly more expensive than Ground Advantage for light items
How to Use USPS Flat Rate Step-by-Step?
- Pick the right size packaging from your post office or order online (free)
- Pack your item carefully and seal the box
- Buy and print your shipping label at USPS.com or via a shipping platform (for commercial rates)
- Drop off the package at a USPS location or schedule a pickup
- Track the shipment via USPS Tracking
Pro Tip: Print postage online using services like Pirate Ship, Shippo, or EasyPost to save on each shipment.
Flat Rate Shipping for Small Businesses
Using flat rate can be a game-changer for ecommerce and small sellers:
- Standardize shipping costs on product pages
- Offer free shipping while maintaining margin control
- Simplify returns by including pre-labeled flat rate packaging
- Integrate with inventory/shipping software for automation
Common Questions About Flat Rate
Do I have to use a USPS-branded box?
Yes. Flat Rate pricing only applies when using USPS-issued Flat Rate packaging.
Can I use Flat Rate for international shipments?
Yes! USPS offers Priority Mail International Flat Rate options.
What if my item doesn’t fit in the box?
You’ll need to use standard Priority Mail or Ground Advantage.
Is Flat Rate always the cheapest?
No. It’s best for dense, heavy items. Compare with Cubic and Ground pricing.
Can I schedule pickups for Flat Rate packages?
Yes, USPS offers free package pickup for Priority Mail shipments.
Should You Use Flat Rate?
Use Flat Rate if:
- Your shipment is heavy and compact
- You want a quick and consistent pricing model
- You want to avoid weight/distance calculations
Avoid Flat Rate if:
- You’re shipping lightweight items (under 1 lb)
- Your product is oversized or doesn’t fit USPS boxes
Flat Rate is a flexible and reliable option for many common shipping scenarios, especially for small business owners, Etsy sellers, and growing ecommerce brands.
Power Up Your Flat Rate Workflow with Willow Commerce
Looking to streamline your USPS shipments? Willow Commerce integrates Flat Rate options directly into your shipping dashboard so you can:
- Print discounted commercial-rate labels
- Sync orders from Shopify, Etsy, and more
- Track shipments in real-time
- Simplify returns with pre-filled labels