# Carrier Packaging

Most carriers support their own package types, each with a specific `package_id` and `package_code` that you define in the `packages` object for a shipment. While the `package_id` and `package_code` properties are not required by ShipStation API, most carriers will require at least the `package_code` to successfully return a label. Additionally, the carrier package you use can affect things like your rate (e.g., a USPS Flat Rate box will have a different rate than a generic package).

To see what types of packages your carrier supports and the associated properties, you can use the [list carrier packages request](/apis/shipengine/docs/reference/list-carrier-packages).

Carrier packaging is distinct from using [custom package types](/apis/shipengine/docs/shipping/custom-package-types), which are custom packages where you define the package properties in advance, including dimensions, and only add the `package_code` to the `packages` object.

## Example Request

This [create label](/apis/shipengine/docs/labels/create-a-label) example uses the USPS Priority Mail service with a medium flat rate box package type. In the case of flat rate boxes, you will declare package weight (to ensure the shipment does not exceed the flat rate maximum) but would not declare package dimensions.

**POST /v1/labels/**


```http
POST /v1/labels HTTP/1.1
Host: api.shipengine.com
API-Key: __YOUR_API_KEY_HERE__
Content-Type: application/json

{
  "shipment": {
    "packages": [
      {
        "package_code": "medium_flat_rate_box",
        "weight": {
          "value": 9.6,
          "unit": "ounce"
        }
      }
    ],
    "service_code": "usps_priority_mail",
    "ship_to": {
      "name": "Amanda Miller",
      "phone": "555-555-5555",
      "address_line1": "525 S Winchester Blvd",
      "city_locality": "San Jose",
      "state_province": "CA",
      "postal_code": "95128",
      "country_code": "US",
      "address_residential_indicator": "yes"
    },
    "ship_from": {
      "company_name": "Example Corp.",
      "name": "John Doe",
      "phone": "111-111-1111",
      "address_line1": "4009 Marathon Blvd",
      "address_line2": "Suite 300",
      "city_locality": "Austin",
      "state_province": "TX",
      "postal_code": "78756",
      "country_code": "US",
      "address_residential_indicator": "no"
    },
    "confirmation": "none",
    "insurance_provider": "none"
  }
}
```

In the creat label response, the `package_code` property will be a property in both the `shipment` object and the `packages` object. In the [create shipment](/apis/shipengine/docs/shipping/create-a-shipment) response, the `package_code` property will be in the `packages` object only.