Cubic Pricing

Cubic pricing calculates shipping costs based on the volume of a package (in cubic feet) rather than its weight. It’s designed for packages that are lightweight relative to their size—where dimensional weight pricing might seem unfair.

How Cubic Pricing Works

Instead of comparing actual vs. dimensional weight, cubic pricing uses tiers based on package volume:

Volume = (Length × Width × Height) ÷ 1,728

This gives you cubic feet, which falls into pricing tiers.

USPS Priority Mail Cubic

USPS offers the most common cubic pricing program:

Requirements:

• Maximum 20 lbs
• Maximum 18" on any side
• Soft-pack or rectangular box
• Commercial pricing only (not retail)

Cubic vs. Other Pricing Methods

When Cubic Pricing Saves Money

Cubic pricing typically wins when:

• Package is under 20 lbs
• No single dimension exceeds 18"
• Contents are lightweight (clothing, crafts, soft goods)
• Shipping to distant zones (5-8)

Example savings:

• 0.3 cubic ft package, 3 lbs, Zone 8
• Priority Mail (weight): ~$15
• Priority Mail Cubic: ~$9
• Savings: 40%

How to Access Cubic Pricing

Cubic rates aren’t available at the post office counter:

• Shipping software: Shippo, Pirate Ship, ShipStation
• USPS Web Tools API: For developers
• Commercial Plus Pricing: Requires USPS account

Calculating Your Cubic Tier

1. Measure package in inches (L × W × H)
2. Multiply dimensions together
3. Divide by 1,728
4. Round up to nearest 0.1 tier

Example:

• Box: 10" × 8" × 6" = 480 cubic inches
• 480 ÷ 1,728 = 0.278 cubic feet
• Tier: 0.3

Cubic Pricing Tips

1. Right-size packaging - Smaller box = lower tier
2. Use poly mailers - Measure at thickest point
3. Compare every time - Not always cheaper than weight-based
4. Stay under limits - 20 lbs, 18" max side
5. Batch by tier - Group similar-sized products