---
title: "How To Ship Flats With Stamps.com"
url: "https://www.stamps.com/article/how-to-ship-flats-with-stamps-com/"
type: "post"
modified: "2025-11-13T15:18:25+00:00"
---
[![How To Ship Flats With Stamps.com_Blog](https://www.stamps.com/wp-content/uploads/2024/05/How-To-Ship-Flats-With-Stamps.com_Blog.jpg)](https://www.stamps.com/wp-content/uploads/2024/05/How-To-Ship-Flats-With-Stamps.com_Blog.jpg)If you need to send a manuscript, set of reports, or sheaf of bills, you’re going to need something a bit larger than a normal letter-sized envelope. The USPS recognizes a category of *Flats* which can comfortably house numerous sheets of paper, magazines, journals, books or other material, without needing to fold the items.

The key thing to remember is that flats must **always** be flexible and uniformly even and smooth with no large bumps. Are you sending a license plate in an envelope? Is your envelope wrapped so tightly in plastic that it can’t even bend anymore? Are you sending a box or parcel? Then none of these mailpieces would be considered flats.

The USPS maintains a consisting standard to determine whether something is considered flexible or not. The official “**flexibility test**” states that a mailpiece is considered flexible “if both ends can bend at least 1 inch vertically without being damaged.” The USPS has a useful [guide](http://pe.usps.com/text/dmm300/201.htm#1096362) that shows you how you can perform your own Flex Test.

The official definition of a flat is that it must have a minimum height of 6-1/8″ and a maximum height of 12″, and a minimum length of 11-1/2″ and a maximum length of 15″. The minimum thickness is ¼” and the maximum thickness is ¾”. Anything exceeding these measurements will be bumped up to the next mailpiece of Thick Envelope/Parcel.

Besides the standards by which there is a minimum and maximum thickness for flats, there are two other regulations to consider:

**– The ¼ Protuberance Rule**
¾ of an inch thick is the maximum thickness for flats, but keep in mind that there is an **additional and separate regulation** regarding uniform thickness. Your flat has to be uniformly thick, so it can’t have any bumps, protrusions, or bulges that cause more than a ¼-inch variance in thickness. Even if your flat is less than ¾ inch thick, it may not always be a flat. If it contains an item inside of it that is creating a bump that is more than ¼ inch thick, then the mailpiece would not be considered a flat. Therefore, the key thing to prevent is from the mailpiece becoming nonuniformly thick with bumps, bulges, lumps, and prominences.

**– Content Shifting**
Because of these thickness and protuberance rules, flats are best used for sending documents, but if you want to use flats for non-paper contents, you should secure the items to prevent shifting. This is because there is an additional postal rule that states that non-paper contents cannot move inside the flat to such a degree that they would create a bump or protrusion, or cause the items to burst out of the flat. The official maximum for content shifting is 2 inches, so your items cannot move inside the flat for more than that distance.

**Sending Flats With Stamps.com**
Stamps.com makes it easy to send to flats! You can print postage for flats in a number of different ways depending on how much information you want on your label.

**\#1. Need just a stamp?**
In your Stamps.com software, select “Stamps” on the left side of the screen and then select “Large Envelopes and Flats” under the drop-down Mailpiece menu. You can then select your mail class as First Class (up to 13 oz.).

**\#2. Want to print postage for a Flat with the delivery and return addresses included?**
In your Stamps.com software, select “Envelopes” on the left side of the screen and then select “Large Envelopes and Flats” under the drop-down Mailpiece menu. You can print to a wide variety of labels, such as SDC-3110 or Avery labels like Avery 32403.

**\#3. Printing First Class, Priority Mail and Priority Mail Express Shipping Labels for Flats?**
Find these mail class options under the “Packages” option on the left side of the screen. Just look for the mailpiece called “Large Envelope/Flat.” These can be printed on plain paper, Stamps.com labels such as the SDC-1200, or Avery labels like Avery 32402. Tracking is available for Priority and Priority Express Shipping Labels for Flats.

How to Ship Flats with Stamps.com (Step‑by‑Step)
------------------------------------------------

Flats (large envelopes) offer a cost-effective way to ship large, thin items through USPS. Follow these steps using Stamps.com:

### **Step 1: Select “Envelopes” and then “Large Envelopes & Flats”**

 In Stamps.com software, click “Envelopes” from the left menu, and under the “Mailpiece” dropdown, choose “Large Envelopes & Flats.”

### **Step 2: Choose your mail class**

 Select First‑Class (up to 13 oz) if you only need postage. For full labels with addresses, select the class under “Packages” and mailpiece type “Large Envelope/Flat.”

### **Step 3: Enter delivery and return addresses**

 Provide the “Ship To” and “Ship From” addresses. Use your contacts or enter manually.

### **Step 4: Enter weight and select service**

 Weigh your flat, then choose the appropriate USPS service and specify package type “Large Envelope/Flat.”

### **Step 5: Print postage or label**

 Click “Print Postage.” You can print on plain paper, Stamps.com label formats (e.g. SDC‑3110), or Avery labels (e.g. 32403). Tracking is available for Priority / Express flats.

### **Step 6: Secure your flat**

 Ensure there are no bulges, protrusions over ¼ inch, and that contents do not shift more than 2 inches inside. Otherwise, it may violate flat rules.