USPS Cubic Pricing Explained: Maximum Savings for Small Heavy Packages

What is USPS Cubic Pricing?

USPS Cubic pricing is a volume-based rate structure that ignores weight for packages under 20 lbs with maximum dimensions of 18x18x18 inches. For small, heavy items, Cubic pricing can save 30-50% compared to weight-based rates.

Cubic Pricing Qualification

Requirements

Requirement	Detail
Maximum weight	20 lbs
Maximum dimension	18" on any side
Services eligible	Priority Mail Cubic (USPS Reseller)
Minimum volume	Commercial agreement required

Cubic Tier Calculation

Formula: (Length × Width × Height) ÷ 1728 = Cubic Feet

Cubic Tier	Size Range	Typical Box
0.10	≤ 0.10 cu ft	4×4×4
0.20	0.11-0.20 cu ft	6×6×6
0.30	0.21-0.30 cu ft	7×7×7
0.40	0.31-0.40 cu ft	8×8×8
0.50	0.41-0.50 cu ft	8×8×8

Cubic vs Weight-Based Pricing

Zone 4 Comparison

Weight	Priority Mail (Weight)	Priority Mail Cubic	Savings
5 lbs	$12.45	$8.25	34%
10 lbs	$18.80	$8.25	56%
15 lbs	$24.50	$8.25	66%
20 lbs	$28.80	$8.25	71%

*Assumes 6×6×6 box (Tier 0.20)

Zone 8 Comparison

Weight	Priority Mail (Weight)	Priority Mail Cubic	Savings
5 lbs	$22.80	$11.45	50%
10 lbs	$35.50	$11.45	68%
15 lbs	$48.20	$11.45	76%
20 lbs	$58.50	$11.45	80%

Cubic Pricing by Tier and Zone

Priority Mail Cubic Rates (Atoship Commercial)

Tier	Zone 1-2	Zone 3	Zone 4	Zone 5	Zone 6	Zone 7	Zone 8
0.10	$5.85	$6.20	$6.85	$7.50	$8.25	$9.45	$10.20
0.20	$6.45	$6.95	$8.25	$9.50	$10.80	$11.85	$13.20
0.30	$7.20	$8.15	$9.85	$11.45	$13.20	$14.50	$16.45
0.40	$8.15	$9.45	$11.50	$13.80	$15.85	$17.45	$19.80
0.50	$9.20	$10.85	$13.25	$15.80	$18.20	$20.50	$23.45

Best Products for Cubic Pricing

Ideal Cubic Products (Small + Heavy)

Product Category	Typical Size	Weight	Tier	Best For Cubic?
Jewelry boxes	4×4×4	1-5 lbs	0.10	✓ Yes
Cosmetics kits	6×6×4	3-8 lbs	0.10	✓ Yes
Supplements (multi-bottle)	8×6×6	5-15 lbs	0.20	✓ Yes
Tools/hardware	8×8×8	10-20 lbs	0.30	✓ Yes
Candles (heavy glass)	6×6×6	3-8 lbs	0.20	✓ Yes
Books	10×8×6	5-15 lbs	0.30	✓ Yes
Gourmet food	8×8×8	8-18 lbs	0.30	✓ Yes

Not Ideal for Cubic (Large + Light)

Product	Typical Size	Weight	Why Not Cubic
Clothing	12×10×4	1 lb	Weight-based cheaper
Pillows	18×18×6	2 lbs	Weight-based cheaper
Stuffed animals	14×14×14	1 lb	Exceeds tier benefit

How to Access Cubic Pricing

Through USPS Directly

Requires Commercial Plus pricing agreement
Minimum volume thresholds (varies)
Account management required

Through Atoship (Recommended)

No minimum volume requirements
Automatic cubic rate application
Best rate selected per package
Immediate access upon signup

Packaging for Cubic Optimization

Box Selection Strategy

Product Weight	Optimal Box	Tier	Strategy
5-10 lbs	Smallest possible	0.10-0.20	Maximize cubic benefit
10-15 lbs	8×8×8 or smaller	0.20-0.30	Significant savings
15-20 lbs	Up to 18×18×18	Any	Still cheaper than weight

Avoid These Mistakes

Oversized boxes: Using 12×12×12 for a product that fits in 8×8×8 wastes tier benefit

Ignoring cubic: Many sellers don't know about cubic pricing

Not measuring accurately: Dimensional measurement is critical

Exceeding 18" limit: Any dimension over 18" disqualifies cubic

Real-World Savings Examples

Example 1: Supplement Seller

Product: 6-bottle vitamin set
Dimensions: 8×6×6 (Tier 0.20)
Weight: 12 lbs
Zone 5 shipment

Rate Type	Cost
Priority Mail (weight)	$32.50
Priority Mail Cubic	$9.50
Savings	$23.00 (71%)

Example 2: Jewelry Business

Product: Watch set with box
Dimensions: 5×5×4 (Tier 0.10)
Weight: 3 lbs
Zone 8 shipment

Rate Type	Cost
Priority Mail (weight)	$18.80
Priority Mail Cubic	$10.20
Savings	$8.60 (46%)

Example 3: Hardware Tools

Product: Socket set
Dimensions: 10×8×6 (Tier 0.30)
Weight: 18 lbs
Zone 6 shipment

Rate Type	Cost
Priority Mail (weight)	$52.80
Priority Mail Cubic	$13.20
Savings	$39.60 (75%)

Monthly Savings Calculator

Monthly Packages	Avg Savings/Package	Monthly Savings	Annual Savings
100	$15	$1,500	$18,000
500	$15	$7,500	$90,000
1,000	$15	$15,000	$180,000
5,000	$15	$75,000	$900,000

Cubic Soft Pack Alternative

For items that can flex:

Uses actual package dimensions (not box)
Same tier structure
Poly mailer or padded envelope
Even smaller cubic calculation

Package Type	Cubic Calculation
Rigid box	L × W × H
Soft pack	Measured when filled

Atoship Cubic Features

Automatic cubic detection: System identifies cubic-eligible shipments
Tier calculation: Accurate cubic tier assignment
Rate comparison: Shows cubic vs weight-based savings
Batch processing: Apply cubic pricing at scale

Start Saving with Cubic Pricing

Create your Atoship account for instant access to USPS Cubic pricing.