Why is my shipping cost calculation incorrect for multiple item orders?

Shopify Discussion

Topic summary

A merchant reports being undercharged for shipping when a customer ordered 3 bundles (9 lbs total). Instead of charging $27 ($9 per bundle), the system only charged $13, forcing the merchant to cover the difference.

Core Issue:
Shopify’s native shipping calculations combine item weights but not dimensions for multi-item orders. When customers buy multiple items requiring separate boxes (e.g., two 16x16x16" boxes at 8 lbs each), the system calculates shipping for one combined package (16 lbs in a single 16x16x16" box) rather than two separate shipments.

Proposed Solutions:

  • Weight-based shipping: Set flat rates that increase per pound/product, though this doesn’t account for dimensional variations
  • Shopify Shipping with USPS calculated rates: Uses actual weights and addresses but still doesn’t handle per-item box requirements
  • USPS Cubic pricing: Available on Shopify Plan and above for small, heavy items under 0.5 cubic feet
  • Third-party apps: Merchants recommend Boxify, which calculates dimensions for multiple products and determines appropriate box configurations

Status:
The issue remains unresolved after 6+ months. Shopify staff acknowledge the limitation and promise to forward feedback to developers, but no native per-item dimensional shipping exists. Merchants must either absorb costs or use paid third-party applications.

Summarized with AI on October 31. AI used: claude-sonnet-4-5-20250929.
19

Hi, @Jcain .

Please know, I truly do want to help you. However shipping is very sensitive and in order to provide a specific answer I must be able to see the abandoned checkout, the shipping profile, the zones, the ships from location, the product/order weight, the default box dimensions, etc.

You can absolutely provide screenshots and I can take a closer look, however, it would serve you well to reach out directly to our live advisors who can easily pull up all the settings that need to be looked at to provide a straight forward answer.

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