USPS Cubic Rates in ShipStation

ShipStation Content Team

Updated November 21, 2023 14:31

USPS offers volume-based cubic pricing. Cubic rates are ideal for small, heavy packages since the pricing is based on the volume of the package instead of the weight. ShipStation can make these rates available to shippers of all sizes.

ShipStation will automatically apply the cubic rate whenever it's cheaper than the Priority rate. This is determined by entering the weight and dimensions of the shipment, then selecting the eligible service. For details on how cubic pricing is calculated, see the section Calculating Cubic for Domestic Priority and Ground Advantage.

The following USPS services are eligible for cubic pricing:

USPS Priority Mail

USPS Priority Mail cubic pricing can apply to small packages that meet the following requirements:

Weighs less than 20 pounds
Measures 0.50 cubic feet or less
Longest dimension does not exceed 18 inches

USPS Ground Advantage

USPS Ground Advantage cubic pricing is the most cost-saving - and slowest - option for shipping packages that meet the following requirements:

Weighs less than 20 pounds
Measures 1 cubic foot or less
Longest dimension does not exceed 18 inches

Receive Cubic Rates in ShipStation

To receive cubic rates in ShipStation:

Choose USPS Ground Advantage (formerly Parcel Select Ground) or a domestic Priority service.
Choose a package type of Package.
Package Requirements

You may use any box that meets the dimensional requirements as long as the following are true:
- The longest dimension does not exceed 18 inches
- Is not a tube or a roll
- Is not a USPS Flat Rate box. Flat Rate boxes must be used with the designated package type selected when creating a label.
Enter the package weight & dimensions. Dimensions must be rounded down to the nearest 0.25 inch.

Once you have entered package dimensions, ShipStation will automatically evaluate your shipments to determine which rate is less: weight-based or volume-based (cubic) rates. The lower of the two will appear as your postage cost.

Calculating Cubic for Domestic Priority and Ground Advantage

The cubic feet measurement for the package is calculated by: [ Length x Width x Height ] / 1728 = Cubic Feet

All measurements should be rounded down to the nearest 0.25 inch.

The appropriate USPS tier will be assigned to the shipment depending on the service type selected.

Domestic Priority Cubic Measurements

Cubic measurements for Domestic Priority has five tiers:

Cubic Price Tiers	Mailpieces Measuring	Cubic Foot
0.1	measuring up to and including	.10
0.2	measuring more than	.10 up to and including .20
0.3	measuring more than	.20 up to and including .30
0.4	measuring more than	.30 up to and including .40
0.5	measuring more than	.40 up to and including .50

Ground Advantage Cubic Measurements

Cubic measurements for Ground Advantage has 10 tiers:

Cubic Price Tiers	Mailpieces Measuring	Cubic Foot
0.1	measuring up to ...	0.1
0.2	measuring more than ...	.10 up to .20
0.3	measuring more than ...	.20 up to .30
0.4	measuring more than ...	.30 up to .40
0.5	measuring more than ...	.40 up to .50
0.6	measuring more than ...	.50 up to .60
0.7	measuring more than ...	.60 up to .70
0.8	measuring more than ...	.70 up to .80
0.9	measuring more than ...	.80 up to .90
1	measuring more than ...	.90 up to 1.00

Cubic Pricing for Soft Packs

USPS offers a special cubic rate option for a package type called Soft Pack or Polybag.

These package types are not yet available in ShipStation, but we plan to make them available in the future.

If you wish to ship using ShipStation Soft Packs, please contact ShipStation support to enable this feature for you.

Both domestic Priority and Ground Advantage require the following to be able to ship using Soft Pack cubic pricing:

The mail piece must be 20 lbs or less.
The longest dimension cannot exceed 18 inches.
May not be in rolls or tubes.

Domestic Priority Soft Pack Measurements

Domestic Priority Soft Pack measurement requirements:

CUBIC PRICE TIERS	Mailpieces Measuring	LENGTH PLUS WIDTH
0.1	from	0" up to 21"
0.2	more than	21" up to 27"
0.3	more than	27" up to 31"
0.4	more than	31" up to 34"
0.5	more than	34" up to 36"

Ground Advantage Soft Pack Measurements

Ground Advantage Soft Pack measurement requirements:

CUBIC-PRICE TIER	Mailpieces Measuring	LENGTH PLUS WIDTH
0.1	from ...	0" up to 16"
0.2	more than ...	16" up to 21"
0.3	more than ...	21" up to 24"
0.4	more than ...	24" up to 26"
0.5	more than ...	26" up to 28"
0.6	more than ...	28" up to 30"
0.7	more than ...	30" up to 32"
0.8	more than ...	32" up to 34"
0.9	more than ...	34" up to 35"
1	more than ...	35" up to 36"

Once enabled, the following steps will allow you to view the appropriate cubic rate for Softpack or Polybag shipments:

Select your order from the Orders grid and choose USPS Priority Mail or USPS Ground Advantage (formerly Parcel Select Ground) as the shipping service.
Set packaging type to Large Envelope or Flat.
Enter the weight of the shipment.
Enter the length and width, but leave the height field blank.

This will fetch the tiered cubic rate for the product, should it meet the requirements for cubic rates.