Guides

Cubic Rating

Learn about cubic rating in the Shipium platform.

Suggest Edits

About cubic rating

Cubic rating is a pricing method used by carriers like USPS that bases the shipping cost on a package's volume rather than its weight. For shippers who send small, dense items, cubic rating can offer significant cost savings.

Shipium's Carrier Selection service automatically determines if a shipment is eligible for cubic rating and compares it against traditional weight-based rates to ensure you always get the most cost-effective option.

📘

API response includes billableCubicVolume

When cubic rating is used, the API response will contain a billableCubicVolume object instead of billableWeight.

Why cubic rating matters

Traditionally, shipping costs are determined by package weight and travel distance (zone). However, a small but heavy package takes up less space on a truck than a large, light one. Cubic rating accounts for this by pricing based on volume (Length x Width x Height).

Key benefits include:

  • Cost savings. If you ship small, heavy products (e.g., books, small electronics, parts), cubic rates are often cheaper than the equivalent weight-based rates.
  • Automated optimization. You don't need to manually calculate cubic rates. Shipium's system handles the complex logic of checking eligibility and selecting the best rate for every shipment.

Configure cubic rate tables

You can include cubic rates in your rate tables alongside standard weight-based rates. Within the Shipium Console, you'll configure rate cards as part of your carrier contract setup for your fulfillment context.

Standard rate cards may be uploaded for any supported carrier. Cubic rate cards may be uploaded for carriers shipping with USPS for part of the delivery transport, including DHL, eHub, OSM, UPSMI, and USPS directly or via EasyPost, Endicia, or Pitney Bowes. If you have both a weight and a cubic rate sheet, you'll see a tab for each type in this section of rate configuration once they're each uploaded.

To have the option to upload rate cards, you will need to select Shipium Costing as your rating type.

  • Upload New Rate Sheet. Optional. You may download a CSV file to complete with the carrier service method rates and upload the CSV file back to the console. When you upload your file, you'll select the type of rate type (weight or cubic) as well as the applicable currency and weight/cubic unit. For packages under the max cubic price tiers of 1.00 cubic foot, a weight-based and cubic rate card may both be applied when rate shopping. When both are applicable, Shipium will calculate both estimated label costs for the package and return the lowest cost rate match between the two.

  • Rate Shopping Cost Modifier. Optional. You may have a cost modifier for this carrier rate. When specified, Shipium will add the amount to the rate calculated for the carrier service method during rate shopping. This value can be a flat rate cost increase or flat rate discount expressed in dollars, or it can be a percentage cost increase or percentage discount expressed as a percentage.

📘

Additional guidance for contract configuration

More information about carrier contract and rate configuration is provided in the Carrier Contracts documentation.

How to identify the billing method

When a shipment is rated by volume (i.e., cubic rating), the billableWeight field in the carrierSelection and carrierLabel objects will be null. When a shipment is rated by weight (i.e., billable weight), the billableCubicVolume field in the response will be null.

Sample API response for cubic rate

This example shows the response for a shipment where a cubic rate was selected.

{
    "shipiumShipmentId": "1175000b-2f8f-4787-a3a7-49b9a3ed8fa8",
    ...
    "carrierSelection": {
        "carrierSelectionId": "5b7be9e9-0379-4db4-a511-bc6299dd612a",
        ...,
        "calculatedBillableWeight": null,
        "calculatedBillableCubicVolume": {
            "cubicVolumeUnit": "ft",
            "cubicVolume": 0.2
        }
    },
    "carrierLabel": {
        "shipiumLabelId": "140cf7bb-0e71-4d23-a350-090a88aa0432",
        ...,
        "billableWeight": null,
        "billableCubicVolume": {
            "cubicVolumeUnit": "ft",
            "cubicVolume": 0.2
        }
    }
}

Resources

Your Shipium team member is available to help along the way. However, you might find these resources helpful:

FAQ

Q: Why is billableWeight suddenly null for some of my shipments?
A: This happens when a shipment is rated using cubic volume instead of weight. This is a standard practice for services like USPS Cubic. Since the shipping cost is based on volume, there is no "billable weight," and the API correctly returns null for that field.

Updated 5 days ago