Flat Rate shipping/boxes that stay predictable at every order volume

Flat Rate packaging only shows when you select USPS Priority Mail as your service, so your team doesn’t waste time hunting for the right menu. Once enabled, your package drop-down can include common flat rate boxes and envelopes, like:

• Small Flat Rate Box, Medium Flat Rate Box, Large Flat Rate Box
• Flat Rate Envelope, Legal Flat Rate Envelope, Padded Flat Rate Envelope

That “pick a package type, get a predictable rate” flow is the whole point of USPS Flat Rate, and we keep it right inside the label screen.

Flat Rate works great for some shipments and is a bad deal for others, so instead of guessing, you can build automation rules that steer each order toward the best option based on weight, destination, SKU patterns, or order tags. Dense items can default to a medium Flat Rate box, light orders can rate-shop against USPS Ground Advantage®, and far destinations can compare Priority Mail Flat Rate against other carriers. You set the logic once—ShipStation handles the sorting from there.

Flat Rate only saves time if your shipping floor moves. We help you go from paid order to printed label without extra clicks. Batch printing keeps your day tight, even when you’re shipping across multiple channels. Run common tasks in the same flow:

• Print labels in bulk, then print packing slips
• Generate an end-of-day form when it fits your carrier workflow
• Schedule pickups for UPS® or USPS from inside ShipStation

Pair that with ShipStation Connect, and your pack station can print to a 4×6 thermal label printer with no driver setup.

USPS Flat Rate is one path to predictable cost. Other carriers also offer flat pricing programs, like UPS Simple Rate, along with their own packaging and rules. In ShipStation, you can rate-shop across services without treating Flat Rate like a separate project. You’ll see rates side-by-side, then choose what matches the order:

• Fast delivery when the customer paid for speed
• Lower shipping costs when margin is tight
• A package option that fits the items without wasted space

One screen. Clear choices. Less second-guessing.

International Flat Rate can work well for certain shipments, but cross-border adds paperwork and compliance. ShipStation handles key label details in the same workflow where you pick your service, including electronic customs declarations when the carrier supports it. As of September 1, 2025, USPS requires a six-digit HS code on customs declarations for each item on international commercial shipments. You can also access services like GlobalPost™, where duties and taxes may be paid by the recipient (DDU) or by you (DDP) for select destinations. Tracking availability varies by service, but labels include a tracking number when the carrier provides one.

Flat rate decisions get messy when orders live in different dashboards. We pull them into one queue so your rules can apply consistently, even when you sell everywhere. Connect Shopify, Amazon, eBay, Etsy, Walmart, WooCommerce, and BigCommerce, then keep fulfillment in one place.

That matters for real operations:

• Multi-channel businesses that need one packing workflow
• Amazon FBA and Amazon FBM sellers who want orders tagged and split by rule
• Teams that want tracking pushed back automatically after label purchase

You ship faster when your orders aren’t scattered.

The label isn’t the end of the job. Tracking is where customers judge you. We let you replace carrier-branded tracking with your own branded tracking page and proactive notifications, so fewer people ask where their package is.

Use it for:

• “Shipped” and “delivered” updates that match your brand
• One tracking link your support team can trust
• Clear status for every order, even when you mix flat rate boxes with other shipping services