Dimensional Weight Calculator
Enter a box size and weight to see the dimensional (DIM) weight and the weight you will be billed at UPS, FedEx and USPS, side by side. It uses the 2026 rules, including the USPS switch to a 139 divisor on July 12, 2026.
Each side is rounded up to the next whole inch, and DIM weight up to the next pound, as UPS, FedEx and USPS now do. USPS only applies DIM weight above 1,728 in³ (1 cubic foot).
DIM weight at ÷139 (FedEx, UPS Daily, USPS)
24 × 18 × 12 in = 5,184 in³
“Billed” = the greater of actual and DIM weight. USPS shows n/a when the box is 1 cubic foot or less.
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Estimates only. Negotiated contracts can use a different divisor — check yours.
The dimensional weight formula
billed weight = the greater of DIM weight and actual weight
Example (loaded above): a 24 × 18 × 12 in box that weighs 10 lb. The cubic size is 5,184 in³. Divided by 139, that is 37.3, so the DIM weight is 38 lb. FedEx, UPS Daily Rates and USPS all bill it as 38 lb, not 10. UPS Retail Rates divide by 166 and bill 32 lb.
UPS, FedEx and USPS rules in 2026
| Carrier | Divisor | When it applies |
|---|---|---|
| FedEx | 139 | US, Puerto Rico and international shipments |
| UPS Daily Rates | 139 | All domestic and international package services |
| UPS Retail Rates | 166 | Retail (counter) prices |
| USPS | 139 | Only boxes over 1,728 in³; Priority Mail Express, Priority Mail, Ground Advantage, Parcel Select |
Sources: UPS and FedEx help pages; USPS FAQ and Federal Register notice 2026-09785. Contract rates can use a different divisor, so check your own agreement. The rules are explained carrier by carrier in UPS, FedEx and USPS dimensional weight rules.
What changed at USPS on July 12, 2026
USPS used to divide by 166 and round each side to the nearest inch. It now divides by 139 and rounds every side up, like UPS and FedEx. The 24 × 18 × 12 in box above was billed at 32 lb by USPS before the change and 38 lb after, about 19% more. Boxes of 1 cubic foot or less are still priced on actual weight.
Why rounding up costs you
Carriers measure to the next whole inch, so a box of 16.2 × 12.1 × 10.4 in counts as 17 × 13 × 11 in. That is 2,431 in³ and 18 lb at ÷139. Measured exactly, it would be 14.7 lb, or 15 lb. Three pounds of the bill come from fractions of an inch. UPS's measuring guide and FedEx's published rules both say to round up, and USPS has done so since July 2026. FedEx's US help page still says “nearest whole inch,” so this calculator rounds up to give the higher, safer number.
How to lower your dimensional weight
- • Use the smallest box that fits. One extra inch on any side is billed across the whole box.
- • Buy boxes in whole-inch sizes, measured on the outside, so rounding adds nothing.
- • Ship soft goods in poly mailers instead of boxes where the product allows.
- • At USPS, stay at 1 cubic foot or less. A 12 × 12 × 12 in box (1,728 in³) is priced on actual weight. Make it 12 × 12 × 13 in and it jumps to 14 lb DIM.
Metric and international shipments
139 in³ per lb works out to about 5,000 cm³ per kg, and 166 to about 6,000. So a US divisor of 139 matches the 5,000 used by express couriers such as DHL Express, and 166 matches the 6,000 used for air cargo. For centimeters and kilograms, use the volumetric weight calculator. For pallets and freight by air, sea, road or rail, use the chargeable weight calculator.
Frequently asked questions
How do you calculate dimensional weight?
Round each side of the box up to the next whole inch, multiply length × width × height, and divide by the carrier's divisor (139 for FedEx, UPS Daily Rates and USPS). Round the answer up to the next pound. You pay on whichever is higher: that number or the actual weight.
What is the FedEx dimensional weight formula?
Length × width × height in inches, divided by 139, for US, Puerto Rico and international shipments. FedEx rounds the answer up to the next whole pound. A 24 × 18 × 12 in box is 5,184 cubic inches, so its DIM weight is 5,184 ÷ 139 = 37.3, billed as 38 lb.
How does UPS calculate dimensional weight?
UPS divides the cubic size in inches by 139 on Daily Rates and by 166 on Retail Rates, then raises any fraction to the next whole pound. It says dimensional weight may apply to all of its domestic and international package services, whatever the box size.
How does USPS calculate dimensional weight?
Since July 12, 2026, USPS rounds each side up to the next whole inch, multiplies them, and divides by 139 if the result is over 1,728 cubic inches (1 cubic foot). Before that date it divided by 166. It applies to Priority Mail Express, Priority Mail, USPS Ground Advantage and Parcel Select. If the DIM weight is over 70 lb, you pay the 70 lb price.
Does dimensional weight apply to small boxes?
At USPS, no: boxes of 1 cubic foot (1,728 cubic inches) or less are priced on actual weight. UPS and FedEx can apply it to any box, so a light 12 × 12 × 12 in box can be billed at 13 lb with them.
Is dimensional weight the same as volumetric weight?
It is the same idea. "Dimensional weight" is the US term, worked in inches and pounds. "Volumetric weight" is the usual term for international and air shipments, worked in centimeters and kilograms with divisors like 5,000 or 6,000.