How-to · Planning model · Updated August 4, 2026
How much does USPS shipping cost?
Direct answer
USPS cost = service + billable weight + zone (plus extras like insurance). Planning example for a 12×10×8 in box, zone 4: Priority Mail at 5 lb ≈ $13.54; Ground Advantage at 5 lb ≈ $7.95. Always confirm on usps.com.
Planning examples (zone 4)
Custom box 12×10×8 in unless noted. DIM divisor 166 in this model. Not official postage.
| Service / package | Weight | Billable (model) | Est. cost |
|---|---|---|---|
| Priority Mail (custom) | 5 lb | 6 lb | $13.54 |
| Priority Mail (custom) | 10 lb | 10 lb | $17.27 |
| Ground Advantage (custom) | 5 lb | 6 lb | $7.95 |
| Priority Small Flat Rate box | 5 lb example | Flat rate | $9.75 |
| Priority Medium Flat Rate box | 20 lb example | Flat rate | $16.25 |
How billable weight works
- Actual weight — scale pounds, usually rounded up for postage.
- Dimensional weight — (L × W × H) ÷ 166 for many USPS retail parcels.
- Billable — typically the higher of the two (unless Flat Rate packaging).
Example: 12×10×8 → 960 ÷ 166 ≈ 6 lb DIM in this model. If your scale weight is lower, DIM can still set the price.
Use the free calculator
Adjust dimensions, zone, service, and extras: USPS shipping cost calculator. Related: dimensional weight, freight cost estimator.