Dimensional Weight Calculator

How dimensional weight works

Parcel carriers sell space in a truck or aircraft, and a large light box uses space it does not pay for by weight. So they work out a second, notional weight from the box's size, the dimensional (DIM) weight, and bill whichever is higher. This calculator applies each carrier's published divisor and, just as important, its rounding rules:

1. Measure length, width and height at the longest points, including any bulge.
2. Round each dimension the way the carrier does: UPS to the nearest whole inch, FedEx and USPS up to the next whole inch.
3. Multiply them for the cube, then divide by the carrier's divisor.
4. Round the result up to the next whole pound (or the next half kilogram for metric billing).
5. Billable weight is the greater of that and the actual weight, also rounded up.

USPS only applies dimensional weight to parcels over one cubic foot. UPS, FedEx and DHL Express apply it to every package.

Current divisors, domestic and international

For UPS and FedEx the divisor is the same for US domestic and international shipments: 139 in³/lb, or 5,000 cm³/kg when you measure in centimetres and bill in kilograms. The two figures are close but not identical (5,000 cm³/kg works out to 138.4 in³/lb), so a box can land half a kilo apart depending on the system the account bills in. UPS's higher 166 applies to Retail Rates, the prices you pay at a counter or without an account.

The big 2026 change was at USPS: from July 12, 2026 the divisor for rectangular parcels dropped from 166 to 139 and fractional inches round up, which puts USPS on the same footing as UPS and FedEx for boxes over a cubic foot. Contract customers of any carrier may have a different, negotiated divisor; use the custom option for that.

Worked example: one box, five answers

An 18 × 14 × 12 inch box weighing 10 lb (3,024 in³):

• UPS Daily Rates: 3,024 ÷ 139 = 21.76, billed at 22 lb.
• UPS Retail Rates: 3,024 ÷ 166 = 18.22, billed at 19 lb.
• FedEx: 22 lb, the same as UPS Daily Rates because the dimensions are already whole inches.
• USPS: the box is over 1,728 in³, so 3,024 ÷ 139 applies: 22 lb. Before July 2026 it would have been 19 lb.
• DHL Express, measured in metric as 45.72 × 35.56 × 30.48 cm: 49,554 cm³ ÷ 5,000 = 9.91, billed at 10 kg (22.05 lb).

Now make the box 17.6 × 14 × 12 inches. UPS rounds 17.6 to 18 and still bills 22 lb; FedEx rounds up to 18 and also bills 22 lb. Bring it to 17.4 inches and UPS rounds down to 17 (2,856 in³, 21 lb) while FedEx still rounds up to 18. Small changes in box size move carriers differently.

Mistakes that turn into DIM adjustments

• Quoting with the wrong divisor. A quote at 166 and a bill at 139 is a 19 % jump in billable weight on every large light parcel.
• Measuring the flat box, not the packed one. Overfilled cartons bulge. Carriers' dimensioners measure the highest point.
• Shipping air. A box two inches bigger than it needs to be in each direction typically adds 40–60 % to the cube. Right-size cartons or switch light, soft goods to poly mailers.
• Ignoring rounding. A 12.1 inch side is 13 inches at FedEx and USPS. Design boxes to whole inches, not just under them.
• Forgetting the size surcharges. Dimensional weight is only part of it. Long or large packages also trigger additional-handling and oversize charges that this calculator does not include.