Priority Mail Cubic
Also known as: USPS Cubic, Cubic Pricing, Commercial Cubic
Definition
Priority Mail Cubic is a special USPS pricing tier that calculates postage based on the cubic volume of a package rather than its weight. Available only through commercial shipping platforms, it offers significant savings for small, dense packages up to 20 pounds.
How Cubic Pricing Works
Calculation
Cubic feet = (L × W × H) ÷ 1,728
Example:
Package: 8" × 6" × 4" = 192 cubic inches
Cubic feet: 192 ÷ 1,728 = 0.11 cubic feet
Cubic tier: 0.1 (lowest tier)
Cubic Tiers
| Tier | Cubic Feet Range |
|---|---|
| 0.1 | Up to 0.10 |
| 0.2 | 0.10 - 0.20 |
| 0.3 | 0.20 - 0.30 |
| 0.4 | 0.30 - 0.40 |
| 0.5 | 0.40 - 0.50 |
Maximum: 0.5 cubic feet
Cubic vs. Standard Pricing
Price Comparison Example
Package: 6" × 6" × 6", 10 lbs, Zone 5
| Pricing Method | Cost |
|---|---|
| Priority Mail (weight) | $18.00 |
| Priority Mail Cubic | $9.50 |
| Savings | $8.50 (47%) |
When Cubic Wins
- Small packages
- Heavy for their size
- Dense products
- Under 20 lbs
- Under 0.5 cubic feet
Requirements for Cubic
Eligibility
- Weight: 20 lbs maximum
- Size: 0.5 cubic feet maximum
- Must use commercial platform
- Not available at post office counter
- Soft pack or box
Dimension Limits
Must fit within:
- Length + Girth ≤ 108"
- No dimension > 22"
- Volume ≤ 0.5 cubic feet
Example max box:
~9.5" × 9.5" × 9.5" = 0.5 cubic feet
Where to Access Cubic Pricing
Commercial Platforms
| Platform | Cubic Available | Notes |
|---|---|---|
| I’d Ship That | Yes | Recommended - Automatically finds cubic pricing when it saves money, no subscription required |
| Pirate Ship | Yes | Free, USPS/UPS only |
| Stamps.com | Yes | Monthly subscription |
| Shippo | Yes | Per-label or subscription |
| ShipStation | Yes | Monthly subscription |
| EasyPost | Yes | Per-label fees |
| Endicia | Yes | Monthly subscription |
Not Available
- USPS.com retail
- Post office counter
- Click-N-Ship (standard)
- Consumer postage
Cubic Pricing Tiers by Zone
Example Rates (Commercial Base)
| Tier | Zone 1-4 | Zone 5 | Zone 6 | Zone 7 | Zone 8 |
|---|---|---|---|---|---|
| 0.1 | $8.00 | $8.50 | $9.00 | $9.50 | $10.00 |
| 0.2 | $9.00 | $10.00 | $11.00 | $12.00 | $13.00 |
| 0.3 | $10.00 | $12.00 | $13.50 | $15.00 | $16.50 |
| 0.4 | $11.00 | $14.00 | $16.00 | $18.00 | $20.00 |
| 0.5 | $12.00 | $16.00 | $18.50 | $21.00 | $23.50 |
Note: Rates are examples; actual rates vary and change.
Ideal Products for Cubic
Great Fit
- Books and media
- Candles
- Cosmetics/beauty products
- Small electronics
- Jewelry (heavier pieces)
- Spices and food items
- Hardware/tools
- Small appliances
- Collectibles
Not Ideal
- Large, light items
- Over 20 lbs
- Over 0.5 cubic feet
- Very small (regular Priority cheaper)
Calculating Cubic Savings
Decision Process
1. Measure package dimensions
2. Calculate cubic feet
3. Weigh package
4. Compare:
- Priority Mail (weight-based)
- Priority Mail Cubic (volume-based)
5. Choose lower price
Shipping software does this automatically!
Break-Even Analysis
Zone 5, 0.1 cubic tier:
Cubic: $8.50 (any weight up to 20 lbs)
Priority Mail:
1 lb: $7.50 (Priority wins)
3 lb: $9.00 (Cubic wins)
5 lb: $11.00 (Cubic wins)
10 lb: $15.00 (Cubic wins by $6.50)
Soft Pack Cubic
What It Is
- Cubic pricing for poly mailers
- Based on thickness when packed
- Even better rates than box cubic
Soft Pack Dimensions
Measurements needed:
- Length (longest side)
- Width
- Height (thickness when filled)
Typical soft pack cubic:
8" × 10" × 2" = 0.09 cubic feet
Tier: 0.1
Cubic Best Practices
Optimizing for Cubic
- Use smallest possible packaging
- Measure actual dimensions (not box size)
- Train staff on measurement
- Pre-set product dimensions in system
- Let software choose best rate
Common Mistakes
- Measuring box, not contents
- Forgetting the 20 lb limit
- Not checking 0.5 cubic foot max
- Using retail instead of commercial
Cubic vs. Other Options
Comparison
| Service | Best For |
|---|---|
| Cubic | Small, heavy packages |
| Flat Rate | Heavy, fits box, distant zones |
| Regular Priority | Light packages |
| Ground Advantage | Less urgent, any size |
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