Package Dimension Calculator
Calculate dimensional weight and shipping estimates for packages.
Compare USPS, UPS, and FedEx size limits and find the best carrier for your box dimensions.
Package Dimensional Weight is used by carriers to price shipments based on volume, not just actual weight. If the dimensional weight exceeds the actual weight, you pay based on the dimensional weight.
Dimensional Weight Formula:
Dim Weight (lbs) = (L × W × H) / DIM Factor
DIM Factors:
| Carrier | DIM Factor (inches) | DIM Factor (cm) | Applies to |
|---|---|---|---|
| USPS | 166 | 5,000 | packages over 1 cubic foot only |
| UPS | 139 | 5,000 | every package |
| FedEx | 139 | 5,000 | every package |
That last column matters more than the divisors do. USPS only applies dimensional weight to packages over one cubic foot (1,728 cubic inches). Below that it bills the actual weight however bulky the carton is, while UPS and FedEx start charging for the empty space immediately. On a small but light box, USPS is not merely cheaper per pound, it is charging for a different, smaller number of pounds.
Girth Calculation:
Girth = 2 × (Width + Height)
Length + Girth = Length + 2 × (Width + Height)
Carriers limit “length + girth”. The longest side is the length, and the other two sides form the girth. This calculator sorts your three numbers for you, so it does not matter which box you type them into.
Carrier Size Limits:
| Carrier | Max Length + Girth | Max Length | Max Weight |
|---|---|---|---|
| USPS Priority | 108 in (274 cm) | 108 in | 70 lbs (31.8 kg) |
| USPS Ground | 130 in (330 cm) | 108 in | 70 lbs (31.8 kg) |
| UPS | 165 in (419 cm) | 108 in | 150 lbs (68 kg) |
| FedEx | 165 in (419 cm) | 119 in | 150 lbs (68 kg) |
Billable Weight:
Billable Weight = MAX(Actual Weight, Dimensional Weight)
The carrier charges whichever is greater.
Practical Example: A box 24 × 18 × 12 inches, actual weight 8 lbs:
- UPS dim weight: (24 × 18 × 12) / 139 = 37.3 lbs
- Billable weight: 37.3 lbs (not 8 lbs!)
- Girth: 2 × (18 + 12) = 60 inches
- Length + girth: 24 + 60 = 84 inches, within every carrier limit in the table
In metric: 61 × 46 × 30 cm, 3.6 kg actual:
- Dim weight: (61 × 46 × 30) / 5000 = 16.8 kg
- Billable weight: 16.8 kg
Tips:
- Use the smallest box possible to minimize dimensional weight charges.
- If your item is light but bulky, dimensional weight pricing can significantly increase cost.
- Flat-rate boxes (USPS) ignore dimensional weight entirely, which is what makes them so good for heavy, small items.
- Always measure the outside of the box, including any bulges.
- Round up each dimension to the nearest inch (or cm) as carriers do.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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