USPS Cubic Pricing is based on the total volume of the package. Packages that are eligible for USPS cubic pricing must have a total weight less than 20 lbs. and a total cubic volume at or below 0.5 cu ft. including packing materials.
Packing materials usually take up 2 inches on each side and can cause the cubic volume to more than double for a package.
Here is how you would calculate whether a package will be below 0.5 cubic feet:
1. Suppose you have a bundle of products whose total cubic volume is 0.2 cubic feet. This value must be converted to cubic inches. 1 cubic foot = 1728 cubic inches. Therefore, 0.2 cubic feet = 345.6 cubic inches.
2. Next, take cube root of 345.6 = 7.02 (rounded up to the second decimal point).
3. Add 2 inches to account for packing materials. Therefore, each side becomes 9.02 inches.
4. 9.02 x 9.02 x 9.02 = 733.87 cubic inches or 0.425 cubic feet (733.87/1728)
5. Rounded up, you have 0.5 cubic feet.
TIP: To check if your package is eligible for cubic pricing,
make sure the total cubic volume of your products are at or
below 0.23 cu ft.