USPS Rate Calculations


This article explains USPS rate calculations in Shipbridge.

USPS Cubic Rates

You must ship over 50,000 packages a year to qualify for USPS Cubic Pricing.

ShipBridge lets you calculate USPS rates, including cubic pricing. USPS Cubic Pricing provides discounted rates to high volume shipping customers for small, heavy packages. Priority Mail packages measuring less than 20 lbs in weight and 0.5 cubic feet in volume, with no dimension longer than 18 in, are eligible for Cubic Pricing as long as you meet the minimum package requirements. For these packages, customers will pay shipping costs for the actual size of the package and the shipping distance instead of its weight.

Compared to other shipping carriers, like FedEx or UPS, which only offer pricing based on weight and distance, USPS Cubic Pricing is a great alternative to help lower your shipping costs. To qualify for Cubic Pricing, customers must ship over 50,000 packages a year. 

You can enable rate calculations through USPS Web Tools in a few short steps. If you have signed up with Endicia ELS, you can also get rates and address validation through ELS as well.

Calculate Cubic Prices

Shipbridge saves you time by letting you calculate USPS rates, including cubic pricing.

The cubic pricing for your USPS package is measured by calculating: Length x Width x Height / 1728 = Cubic Feet

All measurements should be rounded down to the nearest 0.25 in. No dimension may exceed 18 in.

Once you have the cubic feet measurement, your package will fall into one of the following five tiers:

TierCubic Feet
Tier 1Packages up to .10 cubic feet
Tier 2Packages more than .10 and up to .20 cubic feet
Tier 3Packages more than .20 and up to .30 cubic feet
Tier 4Packages more than .30 and up to .40 cubic feet
Tier 5Packages more than .40 and up to .50 cubic feet
As an example, an 8″ length x 6″ height x 8″ width (Tier 3) package weighing 8 lbs and being shipped to Zone 6 would cost $22.47 using Priority Mail Commercial Base rates. The same package would cost only $10.98 with USPS Cubic Pricing.

To use this cubic pricing in Shipbridge, package dimensions must be included on the shipping label requests. To enable this in Shipbridge:

  1. Go to Menu Options Shipping tab.
  2. Check Populate package dimensions in shipping labels requests.
  3. Click Save.

package dimensions

Enable USPS Rate Calculations & Address Validation

If you have your Endicia Credentials entered in Shipbridge, you do not need to do the following.

  1. Go to 
  2. Fill out all required information > Click Submit. You will see the following message: USPS confirmation cubic pricing
  3. Once you receive the email from the USPS, you can respond to to notify them that testing has been completed. Remember to include your Web Tools User ID and password. 
  4. Enter your new USPS Web Tools ID into the appropriate field on the Shipping Rate API page in your Sellercloud account. 
  5. Test the USPS Web Tools ID via the Action menu. 

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