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.
5

Weight based shipping doesn’t work for large packages. A 16x16x16 packages costs the same to ship whether its 5 pounds or 10 pounds. If someone buys two items with a dimension 16x16x16 inches and 5 pounds each, the shopify will say its a single 16 cubed box weighing 10 pounds when the reality is I need to ship them in 2 separate 16 cubed boxes.

Free shipping does not work when the shipping cost varies from $15 all the way to $45 for the exact same package.

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