How to add product dimensions for Shopify shipping

Updated August 13, 2026 · SMART Shipping Rates (E-TRADE PARTNER)

Shopify admin has no native variant length, width, and height field for app-calculated shipping tables. SMART Shipping Rates & Rules stores those dimensions on the Product dimensions page (also on the Shopify variant page) and supports CSV import and export. You can then use them in calculated rates. Calculated rates need Shopify Carrier Service. Delivery customizations do not.

Weight alone does not describe a pillow, a lampshade, or a boxed side table. Those products are light and large. If variant size is missing, a dimensional-weight rate cannot see the box, and an actual-weight table will undercharge the cart.

The job is to store complete length, width, and height on every variant that needs size-aware shipping, then point a rate at those values. Enter a few by hand, import the rest, and use shop defaults only as a fallback.

Why product dimensions matter

• They let checkout charge bulky-light goods by cube instead of scale weight.
• They power dimensional-weight rates, volume conditions, and length or girth surcharges.
• They keep support answers factual: the box size in the app is the box size in the rate.
• They make catalog gaps visible with a missing-dimensions filter before you go live.

What Shopify can and cannot do natively

Shopify stores variant weight on the product. That is useful, and it is not the same as variant size. There is no native variant L/W/H field for app-calculated shipping tables. SMART stores those three sides per variant so calculated rates can use them.

Setup steps in SMART Shipping Rates & Rules

1. Open Product dimensions. You can also edit the same length, width, and height fields on the Shopify variant page.
2. Use the Missing dimensions filter so you work the gaps first. Enter all three sides. A variant with only one or two sides is still treated as missing.
3. For a large catalog, click Import dimensions. Use columns variant_id, length, width, height, and unit. An empty cell leaves the stored value unchanged.
4. Review the required preview, then confirm Import dimensions. Do not skip the preview.
5. Click Export dimensions when you need a backup or a file to edit and re-import. You can limit the file with Only variants missing dimensions.
6. Open Settings and set Dimensional unit. Optionally fill Default dimensions. That fallback replaces the whole box, even if a variant has only some sides filled in.
7. Create a calculated rate in Shipping rates that uses those dimensions, then test in Checkout simulator before real checkout.

Worked example: pillows, lampshades, and furniture

A home goods merchant sells throw pillows, lampshades, and lightweight furniture. Scale weight is low. The boxes are not. The team wants size on every shippable variant before it turns on dimensional-weight rates.

1. Filter Product dimensions to Missing dimensions and enter the lampshade and side table by hand.
2. Export a CSV, fill the pillow variants, and import with columns variant_id, length, width, height, unit. Example row: 45000000000001,45,45,20,cm.
3. Preview the import, confirm the variant count, then import.
4. In Settings, set a small default box only for accessories that always ship in the same mailer. Leave furniture without a default so a missing table cannot silently inherit a mailer size.
5. Create a dimensional weight shipping rate using Cart dimensional weight so the pillow and lampshade are charged on cube.

You can enter sides in any order. SMART sorts them longest-first when it evaluates rates. Chargeable weight is max(actual weight, volume ÷ volumetric divisor). The divisor lives in Settings, not on the product row.

Tips for a catalog you can maintain

• Treat Product dimensions as source data. Rates only read what is stored there.
• Re-run the Missing dimensions filter after imports. Empty CSV cells do not wipe values, but they also do not fill gaps.
• Set Default dimensions only when a true standard box exists. Whole substitution means a half-filled variant uses the default, not a mix of typed and default sides.
• Align Dimensional unit and Volumetric divisor in Settings before you test DIM rates.
• After dimensions are in place, use dimensional weight rates when packed cost follows cube, not scale weight.

How to test before launch

Pick one pillow, one lampshade, and one furniture variant. Confirm all three sides on Product dimensions, then run those carts in Checkout simulator. Include one variant with no dimensions, and one that should use shop defaults if defaults are set. Repeat the same carts in real checkout. The simulator does not run delivery customizations.

Frequently asked questions