How do Shopify packed dimensions and automatic box selection work?

Updated 2026-10-21. Checked against Shopify's own documentation; links are under Sources.

Packed dimensions are the length, width and height of a product as it ships. When the items in an order have them, Shopify can choose a box for a multi-item order by itself: according to its help, items "are packed into the smallest of your saved boxes that fits them". If any dimensions are missing, or no saved box fits, Shopify uses its existing package-selection behaviour. To use the feature, save your real boxes and add packed dimensions to your products, either one at a time or in bulk through the product CSV.

What changed in 2026

On September 29, 2026, Shopify's developer changelog announced "Manage packed product dimensions with the GraphQL Admin API". It said:

"The packedDimensions field returns the packed length, width, height, and unit for an inventory item."
"Shopify uses these measurements for automatic package selection on eligible multi-item orders."
"If dimensions are missing or no saved package fits, Shopify keeps the existing package-selection behavior."

The API for apps is in Admin API version 2027-01, which was a release candidate when this was written. Stable versions normally arrive in January. That date matters to apps. For merchants, Shopify's product CSV template already has packed-dimension columns, so you can add dimensions in bulk today.

Why it matters for shipping costs

Carrier-calculated rates are based on "weight, dimensions, and destination", so the box matters as well as the weight. Carriers also bill large, light parcels by dimensional weight. If every order is quoted in one large default box, small orders can be overcharged or undercharged at checkout. Choosing the smallest box that fits brings the quote closer to what you actually ship. Our dimensional weight calculator shows how much a box's size can matter.

Step 1: Save the boxes you actually use

Go to Settings › Shipping and delivery and find the packages section.
Add each box or mailer you stock, with its outside dimensions and its empty weight. Shopify adds the package weight "to the weight of the products being shipped".
Choose a default package for orders where automatic selection doesn't apply.

Automatic selection can only choose from boxes you've saved, so a missing size can never be picked.

Step 2: Add packed dimensions to products

Measure each product ready to ship: folded and bagged, or in its own retail box. One measurement usually covers every variant of the same size.

In bulk with the product CSV

Shopify's product CSV template now has four columns for this:

Packed product length
Packed product width
Packed product height
Packed product dimension unit (Shopify's sample file uses cm)

Export from Products › Export. If your export doesn't include the packed columns, copy their headers exactly as they appear in Shopify's template on the CSV help page.
Fill the four columns on each variant row (rows with the same URL handle). Leave image-only rows blank.
While you're there, check Weight value (grams): dimensions without weights still give wrong rates.
Import from Products › Import with the option to overwrite existing products turned on. Try two or three products first and check them in the admin.

The full CSV method, including how to stop Excel damaging barcodes, is in our bulk weights guide.

Things to keep in mind

All or nothing per order. According to the changelog, if any item is missing dimensions, Shopify falls back to its existing behaviour. One unmeasured product can stop automatic selection for every order that includes it.
"Eligible" multi-item orders. The changelog limits this to eligible multi-item orders and doesn't list every condition. Test a few real carts after you set it up.
Measure as shipped, not as listed. A folded sweater in a poly bag is a different size from the garment's listed measurements.
Keep units consistent. Use one dimension unit throughout a file.

Check that it worked

Create a test order with two or three small items that fit together in one of your smaller saved boxes, then look at the package Shopify suggests when you buy a label. Compare the checkout shipping rate with the label price for a few typical carts. If Shopify keeps using the default box, check that every item in the order has all three dimensions and that a saved box is big enough.