Dimensional weight calculator for UPS, FedEx and USPS

Dimensional weight is length × width × height in inches, divided by the carrier's divisor and rounded up to the next pound. Carriers bill the greater of that and the actual weight. This calculator does the math so you can check the billed weight behind a postage charge on your 3PL invoice.

How to use the calculator

Enter the box's length, width and height in inches, measured at the longest points.
Enter the actual weight in pounds.
Choose the carrier and divisor:
- 139: UPS or FedEx daily rates.
- 139: USPS. Dimensional weight applies only to parcels over 1,728 cubic inches, and the calculator checks that for you. This is the USPS rule from July 12, 2026. For a USPS label from before that date, choose Custom and enter 166.
- 166: UPS retail rates.
- Custom if your contract sets its own divisor. Negotiated contracts sometimes do.

The calculator rounds each measurement up to the next whole inch before multiplying, as UPS, FedEx and USPS now do, so a side measured at 12.2 inches counts as 13. You can type measurements with decimals.

The formula

Volume = length × width × height, in cubic inches.
Dimensional weight = volume ÷ divisor, rounded up to the next whole pound.
Actual weight is rounded up to the next whole pound.
Billable weight = the greater of the two.

The carriers' own rules, at the time of writing (October 2026):

Carrier	Divisor	Measurements	When it applies
UPS	139 daily rates, 166 retail rates	Rounded up to the next whole inch	UPS says it may apply to all its domestic and international package services
FedEx	139 for US shipments	Rounded up to the next whole inch from August 18, 2025	When dimensional weight is more than actual weight
USPS	139 from July 12, 2026 (166 before)	Rounded up to the next whole inch from July 12, 2026 (before, rounded to the nearest inch)	Only parcels over 1,728 cubic inches

Two USPS details matter when you check a bill. Dimensional weight applies only above one cubic foot, so a 12 × 12 × 12 inch box (exactly 1,728 cubic inches) is billed on actual weight. And if the dimensional weight is over 70 pounds, USPS charges the 70-pound price.

Worked example

A box measures 16 × 12 × 10 inches and weighs 6.2 pounds.

Volume: 16 × 12 × 10 = 1,920 cubic inches.
With 139: 1,920 ÷ 139 = 13.81, rounded up to 14 lb.
With 166: 1,920 ÷ 166 = 11.57, rounded up to 12 lb.
Actual weight 6.2 lb rounds up to 7 lb.

Billable weight is 14 lb at UPS or FedEx daily rates, and at USPS from July 12, 2026. It would have been 12 lb at USPS before that date. Either way the box bills well above its actual weight.

Rounding makes a real difference. Take a box measured at 12.2 × 10.3 × 6.4 inches, weighing 3.4 pounds:

Rounding	Dimensions	Volume	÷ 139	Dim weight
Up (current UPS, FedEx and USPS rules)	13 × 11 × 7	1,001	7.20	8 lb
To the nearest inch	12 × 10 × 6	720	5.18	6 lb

At UPS or FedEx this box bills at 8 lb, not its actual 4 lb (3.4 rounded up). At USPS it bills at 4 lb, because 1,001 cubic inches is under the 1,728 threshold.

What the result means

Billable weight above actual weight means the box is too big for what is inside. A smaller box or a mailer may bring it down, and that is a packaging choice to discuss with your 3PL.
Billed weight on the invoice higher than the calculator's suggests the box dimensions on file are wrong, or the wrong box was used. Ask for the dimensions recorded for those shipments.
Billed weight that matches means the postage difference, if any, is in the rate or the markup. Check it with the shipping markup calculator.

For more on how dim weight shows up on a 3PL bill, read our page on dimensional weight charges. Wrong box sizes are one of the common 3PL billing errors.

Check every shipment, not one box

3PL Checker's free audit checks postage and surcharges on every shipment on your 3PL invoices against your contract, along with every other charge. A person reviews each finding, and you get the evidence and a credit request ready to send.

Questions

How is dimensional weight calculated?

Multiply length × width × height in inches, divide by the carrier's divisor, and round up to the next whole pound. You pay for the greater of that and the actual weight, also rounded up.

What is the dimensional weight divisor for UPS?

UPS publishes 139 for daily rates and 166 for retail rates. A negotiated contract can set a different divisor, so check yours.

Does USPS use dim weight?

Yes, for Priority Mail, Priority Mail Express, USPS Ground Advantage and Parcel Select parcels over one cubic foot (1,728 cubic inches). From July 12, 2026 USPS divides by 139; before that it used 166.

Do you pay dimensional weight or actual weight?

Whichever is greater. A large, light box is billed on dimensional weight; a small, heavy one on actual weight.