Searching for the lowest cost of the USPS Flat Rate shipping option? The least expensive USPS is the Priority Mail Flat Rate Envelope, which begins at $9.65 retail price. When bought online with commercial prices, it can fall to approximately $8.00-$8.90. The United States Postal Service covers all Flat Rate services and delivers them within 1 to 3 business days with tracking and insurance value of $100.
Flat Rate pricing is only applicable when the official USPS Flat Rate branded package is used and when the package can accommodate up to 70 lbs. and ship anywhere in the U.S. at a fixed price. In this guide, you will find the cheapest USPS Flat Rate envelopes and boxes, their existing commercial prices, and their comparison to decide which is the most cost-effective shipping option.
What are the Cheapest Shipping Options of USPS Flat Rate?
The Priority Mail Flat Rate Envelope (retail $9.65), the Small Flat Rate Box (retail $10.20), and the Padded Flat Rate Envelope (retail $10.40) are the cheapest shipping options available through the USPS. They are best used in cases of heavy goods that are within an official USPS Flat Rate box and can be shipped within 1 to 3 business days around the country at a fixed rate.
Now let's have a look at the details of each packaging option:
1. Priority Mail Small Flat Rate Envelope (Least Expensive in General)
Retail Price: $9.65
Commercial Price (online): ~$8.05–$8.90
Size: 12½″ × 9½″
Max Weight: 70 lbs
This is the most affordable flat-rate product. It is ideal for heavy documents, small dense items, and long-distance shipments. Because the price is not dependent on the zone, it is affordable for shipping nationally.
2. Small Flat Rate Box
Retail Price: $10.20
Commercial Price: ~$8.55–$9.80
Size: 8 11/16″ × 5 7/16″ × 1 3/4″
Max Weight: 70 lbs
It is best for small electronics, tools, jewelry, and compact heavy products. Most of the times this is cheaper than a zone-based Priority Mail pricing, when your item weighs more than 1- 2 lbs and fits inside.
3. Padded Flat Rate Envelope
Retail Price: $10.40
Commercial Price: ~$8.80–$10.20
Size: 12½″ × 9½″
Max Weight: 70 lbs
This is perfect in cases where you require cushioning but still require flat-rate pricing. It works well for clothing, accessories, and small boxed items. It is a little more expensive than the regular envelope but offers built-in protection.
4. Legal Flat Rate Envelope
Retail Price: $10.10
Commercial Price: ~$8.80–$9.90
Size: 15″ × 9½″
Max Weight: 70 lbs
It can be used for large documents, legal paperwork, contracts, and unfoldable certificates. In case you have to send some important documents and keep them flat, this envelope is often cheaper than a box, and it will keep the papers flat as well without folding.
USPS Priority Mail Flat Rate Boxes and Envelopes Price Table (2026)
All services fall under USPS Priority Mail Flat Rate and have a delivery time of 1-3 business days, and $100 insurance.
When is USPS Flat Rate the Cheapest Shipping Service?
Flat Rate is the most cost-effective service when:
- Shipping heavy items
- Shipping packages to different areas (Zones 6 and 8)
- Products are well packaged in a small box or envelope
- You want fixed pricing
Lightweight packages are not normally the cheapest on a flat rate. Standard USPS Priority Mail can be cheaper in that case.
What If Your Package is Too Large to Fit in Flat Rate Packaging?
If your package:
- Does not qualify as flat-rate packaging
- Weighs under 1-2 lbs
- Light in weight, larger in size
USPS Ground Advantage can be less expensive. Ground Advantage prices are determined by weight and zone. In the case of light packages, it may be cheaper than any Flat Rate. The delivery time is usually 2-5 working days, and it does have tracking. Heavy items are good with Flat Rate. Ground Advantage is ideal for lightweight parcels.
Conclusion
The most affordable USPS flat-rate packaging option is the Flat Rate Envelope with a cost of $8.90, and the Small Flat Rate Box with a $9.80 cost at commercial rates. It has a 1-3 day delivery period, tracking, and insurance of $100, and is a good alternative for heavy but small items or items that have to be shipped over a long distance. Select Ground Advantage to ship light packages and save on shipping.
Note: Never buy your label without first comparing weight-based pricing so that you can pay the lowest possible price.
