Is it cheaper to ship flat rate or by weight?
With flat rate shipping, the weight of a package does not affect the cost of shipping. If you ship heavy items, then this will save you money. On the flip side, flat rate shipping can be more expensive if your packages are lightweight.
Cut on shipping costs
With medium and large flat rate boxes offered by the USPS for free, it's a great, cost-cutting option. But be warned: Even though you get these boxes for free, you may end up paying $10 more than when you use your own box and ship with a different USPS service that offers better rates.
It's Perfectly Fine to Change Flat Rate Packaging to Ship Weight-Based Priority Mail. Contrary to popular belief, you can alter your flat rate packaging to qualify for weight-based rates. Typically, it's crucial that you pay for the specific service marked on your USPS box or envelope.
Flat rate shipping may be more economical because shipping costs are not based on weight or dimensional weight, especially for smaller but heavier items.
A good rule of thumb is to ship small, heavy packages via Flat Rate, and large, lightweight items via Priority Mail.
USPS will always be the cheapest way to ship compared to FedEx or UPS hands down. However as the weight creeps closer to 2 pounds, USPS shipping costs achieve pricing parity with UPS and FedEx Ground.
Out of the three major carriers, USPS is typically the cheapest option. After that, UPS comes in at a close second, and FedEx ranks as the most expensive (yet arguably most reliable) carrier. Since it offers the best mix of affordability and service, USPS is the most popular small ecommerce shipping solution.
To ship via Flat Rate, you need to use the Flat Rate branded boxes. To use Cubic and weight-based options, you will need to use your own packaging or USPS Priority Mail boxes.
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.
Free Supplies8 | Shipping Price |
---|---|
Small Flat Rate Box | $8.25 Commercial Base $9.45 at Post Office & Online |
Medium Flat Rate Box — 1 (top-loading) | $14.25 Commercial Base $16.10 at Post Office & Online |
Medium Flat Rate Box — 2 (side-loading) | $14.25 Commercial Base $16.10 at Post Office & Online |
Are flat rate boxes free?
USPS flat-rate boxes are free. Merchants order them at no cost and start shipping. Merchants will still need to purchase packing peanuts or similar cushioning material, but avoiding as much as $1 per box can be huge savings. (Other carriers, I should add, also include free boxes with their flat-rate services.)
While flat rate shipping includes a consistent fee for packages, standard shipping varies more. Standard shipping rates might be applied based on size, shape, weight, distance traveled, or even package type. Each carrier sets their own standard shipping rates.

To offer a flat-rate shipping service, you must calculate the average shipping cost for the whole company. Then, as your costs rise, you can increase the shipping fees, as they fall the cost to your customers will fall.
- Decrease the shipping distance. ...
- Weigh your packages and reduce dimensions. ...
- Find discounted supplies. ...
- Get discounted shipping rates. ...
- Check out offers from the platform(s) or marketplace(s) you sell on. ...
- Insure with third parties. ...
- Go prepaid.
For First-Class Mail, shape and weight will determine the price. For Priority Mail, the price is a combination of weight, size, and how far the mailpiece is traveling. Priority Mail pieces that exceed one cubic foot, are subject to "dimensional weight pricing".
The Priority Mail Flat-Rate Box is priced at $8.95, regardless of weight, contents, or distance traveled. The Priority Mail Flat-Rate Envelope is priced at $4.60 — the same as the (unzoned) 1-pound rate.
17 lbs | $30,28 | 2-4 business days |
18 lbs | $31,86 | 2-4 business days |
19 lbs | $33,42 | 2-4 business days |
20 lbs | $35,06 | 2-4 business days |
21 lbs | $36,53 | 2-4 business days |
If you're shipping a package up to 20 pounds and within a certain volume range (1728 cubic inches), USPS Priority mail is your best option. If your package exceeds these specifications, carriers like FedEx or UPS will most likely be a cheaper option.
UPS and FedEx both offer flat rate shipping for boxes up to 50lbs, often at cheaper rates than variable pricing. UPS flat rate shipping, called UPS Simple Rate, offers delivery as fast as second-day air transport.
How much does USPS shipping cost per pound?
How much does USPS shipping cost per pound? USPS packages cost about $2.74 if less than one pound; if one pound or more, most packages start at $7. USPS rates for packages heavier than one pound typically increase by 10 to 25 cents for each pound added.
Shoeboxes or paperboard boxes should never be used. Remove old address labels, Hazardous Materials indicators such as diamond labels and markings, as well as delivery markings and bar codes from the previous shipment.
Yes, you can reuse Amazon boxes for your next shipping, whether through the post or courier companies! You have to make sure that you cover the previous labels so that the parcel does not end up delivered to another destination.
The limit to priority mail flat rate is 70lbs.