What is Dimensional Weight? 

Dimensional weight is a pricing structure that increases the shipping rate if a parcel is deemed too large in relation to its weight—think things like a spare tire, a big bag of chips, or a hula hoop . Since packages take up space in cargo vehicles and airplanes, etc., their shipping rate increases with their size.

How Dimensional Weight is Calculated

Dimensional weight relies on a formula to create the volumetric weight of a parcel The basic formula is as follows:

(Length x Width x Height) / divisor = Dim. Weight

Dimensional Weight Formula

Carrier

Dimensional Weight Formula

USPS

(L x W x H) / 166

FedEx

(L x W x H) / 139

UPS

(L x W x H) / 139

If this volumetric weight exceeds the parcel’s true weight, then the carrier will charge as though that value were the package’s true weight. 

USPS

USPS charges dimensional weight at a more affordable rate than UPS or FedEx. The divisor for USPS is larger: 166. This creates a lower number, meaning that it is harder for Dimensional Weight pricing to apply to a parcel. For a breakdown of available USPS rates through ShipStation, read our 2026 USPS rates. You can also check rates for your shipments by using our USPS Rate Calculator. 

FedEx

FedEx charges at a higher rate than USPS with a divisor of 139. This causes more parcels to be subject to dimensional weight rates than with USPS. 

UPS

Like FedEx, UPS uses a divisor of 139 when determining the rate for dimensional weight shipping. However, with UPS, it is possible to save on shipping costs. Because of our close partnership, ShipStation offers substantial discounts on UPS shipping rates. 

What are Cubic Rates? 

Cubic rate pricing is the opposite of dimensional weight. It is a way of paying a reduced rate for parcels that are heavy and small. If dimensional weight charges you more for large, heavy packages, cubic rates are the opposite. 

The USPS Cubic Formula

(Length x Width x Height) / 1728 = Cubic weight

Cubic Pricing Tiers:

  • Tier 1: Packages up to .10 cubic feet
  • Tier 2: Packages more than .10 and up to .20 cubic feet
  • Tier 3: Packages more than .20 and up to .30 cubic feet
  • Tier 4: Packages more than .30 and up to .40 cubic feet
  • Tier 5: Packages more than .40 and up to .50 cubic feet

Cubic Rates Available in ShipStation

Cubic Tier

Zone 1 & 2 

3

4

5

6

7

8

9

0.1

$8.62

$8.85

$9.42

$10.23

$10.72

$11.32

$12.03

$22.48

0.2

$8.72

$8.95

$9.52

$10.33

$10.82

$11.42

$12.13

$22.58

0.3

$9.42

$9.74

$10.37

$12.37

$14.66

$15.62

$17.47

$33.08

0.4

$9.58

$10.34

$10.97

$12.42

$15.47

$17.40

$18.50

$39.27

0.5

$9.76

$10.84

$11.76

$16.18

$18.60

$20.00

$22.18

$45.81

While these are discounted rates available to all ShipStation customers, there are additional discounts on cubic available through contract negotiations with the USPS. To view full Cubic rates, head to Stamps.com. 

To start saving on Dimensional Weight and Cubic pricing now, sign up for a ShipStation trialtoday. 

James Messer
James Messer

James Messer is a copywriter specializing in shipping, logistics, and ecommerce.

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