USPS Dimensional Weight Calculator
Calculate USPS dimensional weight using the 166 in³/lb divisor that applies to balloon and large parcels over one cubic foot, then compare it against actual weight.
How USPS dimensional weight works
USPS applies dimensional weight only to larger parcels, specifically packages that exceed one cubic foot (1,728 in³) in certain zones and services. When it applies, the chargeable weight is the greater of actual and dimensional weight:
DIM weight = (L × W × H) ÷ 166
The USPS divisor is 166 in³/lb, which is gentler than the 139 used by FedEx and UPS, a larger divisor produces a smaller dimensional weight. Measure to the longest points, multiply, divide by 166, and round up to the next whole pound.
Worked example (page defaults)
With the default 18 × 14 × 12 in box:
- Cubic size: 18 × 14 × 12 = 3,024 in³, that is 1.75 ft³, so it is over the one-cubic-foot threshold and DIM pricing can apply
- DIM weight: 3,024 ÷ 166 = 18.22, rounded up to 19 lb
If the parcel actually weighs 11 lb, the 19 lb dimensional weight governs. Had this same box shipped via a 139-divisor carrier, it would have computed to 21.75 → 22 lb, the 166 divisor saves three pounds of billable weight.
Divisor reference
| Carrier / service | Divisor | Unit |
|---|---|---|
| USPS (parcels over 1 ft³) | 166 | in³/lb |
| Generic / older standard | 166 | in³/lb |
| FedEx / UPS US domestic | 139 | in³/lb |
| Air freight (IATA) | 6000 | cm³/kg |
The one-cubic-foot rule
The practical trigger for USPS is the 1 ft³ = 1,728 in³ boundary. Anything at or below that size is generally billed on actual weight regardless of shape; once a box crosses it, the 166 dimensional weight comes into play for the affected services and zones. Keeping a parcel just under a cubic foot, where the contents allow, sidesteps DIM pricing entirely. To compare the courier figures head to head, the FedEx dimensional weight calculator and UPS dimensional weight calculator both use the stricter 139 divisor; the base dimensional weight calculator lets you switch divisors, and dimensional weight explained covers the concept in depth.