How do you calculate dimensional weight?

Multiply length × width × height and divide by the carrier’s divisor. In inches the result is in pounds: UPS daily rates, FedEx and USPS use 139. In centimetres the result is in kilograms, and most international express services divide by 5,000.

What is billable weight?

The weight you pay for: whichever is greater of the actual weight and the dimensional weight.

Does USPS always charge dimensional weight?

No. USPS applies dimensional weight only to parcels larger than 1 cubic foot (1,728 cubic inches). Since 12 July 2026 it uses the 139 divisor for Priority Mail, Ground Advantage and Parcel Select.

Do carriers round the measurements?

Yes. UPS, FedEx and USPS round each side up to the next whole inch and the result up to the next pound. Keep the rounding option on for the closest match.

Dimensional Weight Calculator | DIM Weight for UPS, FedEx, USPS

How dimensional weight works

Carriers charge for the space a parcel takes up as well as its weight. They work out a dimensional weight from the box size and bill whichever is greater: actual or dimensional weight. Light, bulky parcels are billed on size.

Formula

Inches / pounds: L × W × H ÷ 139 (UPS daily rates, FedEx, USPS) or ÷ 166 (UPS retail rates)
Centimetres / kilograms: L × W × H ÷ 5,000 (most international express services)
Billable weight: the greater of actual weight and dimensional weight

Example

An 18 × 14 × 10 inch box is 2,520 cubic inches. Divided by 139 that is 18.1 lb, so it is billed at 19 lb, even if it weighs only 6 lb.

Cutting shipping costs

The quickest win is a box that fits the product; the "trim each side" line in the calculator shows the difference. To set up shipping rates and free shipping in your store, see how to set up free shipping on Shopify, and to budget for shipping alongside other costs use the Shopify store cost calculator.