Guide to USPS Flat Rate shipping for sellers

Flat Rate shipping is a USPS Priority Mail option that charges a fixed price per shipment. On Whatnot, sellers can turn on Flat Rate for shipments between 1 and 70 pounds. It’s a simple way to offer predictable shipping costs.

This is different from regular Priority Mail, where shipping costs vary based on the package’s weight, size, and distance.

On this page: 

• When you can use Flat Rate
• Why sellers use Flat Rate
• How much Flat Rate costs
• Turn on Flat Rate shipping
• Flat Rate packaging requirements
• Tips for shipping with Flat Rate 

When you can use Flat Rate 

You can use Flat Rate shipping on Whatnot if:

• You’ve turned on Flat Rate shipping
• You’re shipping domestically within the US
• The order was made during a show
• The shipment weighs more than 1 pound (up to 70 pounds)
• You’re using USPS Flat Rate packaging 

Not available for:

• Shipments under 1 pound
• Orders placed outside of shows

Why sellers use Flat Rate

• Simple, fixed cost per shipment
• Free packaging from USPS
• Great for heavier items that fit in small or medium boxes

How much Flat Rate costs

Each Flat Rate label costs $9.21 ($8.77 + fees*). 

This cost is charged per shipment, not per show or per buyer. For example, if a buyer places multiple orders during a show and the items ship separately, each Flat Rate shipment will cost $9.21.

*Note: The total shipping prices includes the label price plus a small fee to help cover the operational cost of features like Smart Bundling™ and Flat Rate shipping. Whatnot continues to invest in great product experiences and work with our carriers to get preferential rates for our customers.

Turn on Flat Rate shipping

You can turn on Flat Rate shipping for all future shows, a specific show, or an individual shipment.

Turn on Flat Rate for future shows

Flat Rate will apply to all eligible orders placed during future shows.

Turn on Flat Rate for a specific show 

Flat Rate will apply to eligible orders in a single show, and will carry over to future instances if the show repeats. 

On a computer? You can also update shows from the Seller Hub > Shows page at whatnot.com.

Turn on Flat Rate after a sale 

If you forgot to enable Flat Rate before your show, you can still adjust the shipment before generating the label. Note: Shipping costs won’t be refunded if you switch to a lower-cost label.

Flat Rate packaging requirements

To qualify for Flat Rate pricing, you must use official USPS Flat Rate packaging. You can get free boxes and envelopes from your local USPS, or order online at usps.com.

Accepted packaging:

• Flat Rate Boxes (Small, Medium, Large)
• Flat Rate Envelopes (Regular, Legal, Padded)

Don’t use:

• Packaging that’s not labeled for Flat Rate service
• Your own boxes or envelopes
• Priority Mail, Ground Advantage, First-Class, or Media Mail packaging

If you have a Flat Rate label but don’t use eligible packaging, USPS may reject the package or charge extra postage later. 

Tips for shipping with Flat Rate 

• Flat Rate is a type of USPS Priority Mail with one fixed price for packages 1–70 lbs
• The fixed price applies per shipment, not per buyer or show
• Flat Rate works best when Smart Bundling™ is allowed — avoid custom shipping profiles with a max bundle size
• Make sure bundled items fit in your Flat Rate box, or you may need a different label
• Adjusting the shipping method after a sale may cause label price to change based on weight and distance