Why are my Shopify shipping rates wrong? (Products missing weight)

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

If shipping is cheaper at checkout than the label you buy, check product weights first. Shopify's help says "A product with no weight is treated as weightless, so a cart can fall into a lower weight tier than you expect", and that when products are missing weight, "shipping rates don't calculate correctly at checkout". Find every variant with a weight of 0, enter the real weight, and then look at your package settings.

How Shopify uses weight to price shipping

Weight-based rates (rates you set in a shipping profile, such as "0–1 kg: $5"): Shopify works out the cart's weight from the individual products and picks the matching rate. Weightless items add nothing, so a heavy order can still get the lightest rate.
Carrier-calculated rates: Shopify's help says "The carriers determine the rates based on the order details, including weight, dimensions, and destination". With a missing weight, the carrier quotes for a lighter parcel than the one you'll actually ship.
Package weight: Shopify adds the weight of your default package: "the weight of this package is added to the weight of the products being shipped". So a cart full of weightless products is still priced at the box weight, which makes the error easy to overlook.

Step 1: Find the variants with no weight

The admin has no single screen listing variants with a weight of 0, so use an export:

Go to Products › Export, choose All products and a CSV format.
Choose the file in the product CSV checker. Under "Missing weight", it lists every variant that requires shipping but has a Weight value (grams) that's empty or 0. Gift cards and variants not marked as requiring shipping are skipped.

If you'd rather use a spreadsheet, filter the Weight value (grams) column for 0 or blank, and the Requires shipping column for true. Older exports call these Variant Grams and Variant Requires Shipping.

Step 2: Enter real weights

A few products: open the product in Products and go to the shipping section. The weight field only appears when the setting for "a physical product that you ship" is on. Enter the weight of one unit. Shopify notes that the weight "needs to be exact because it's used to calculate shipping rates".
Many products: edit the Weight value (grams) column in the export and import it again. Step-by-step bulk guide.

Weigh one unit of each product on a kitchen or shipping scale. Variants of the same size usually weigh the same, so one measurement often covers a whole product type. The shipping weight helper converts between g, kg, oz and lb, and has rough ranges for spotting obvious mistakes, such as a hoodie at 5 g.

Step 3: Check your package settings

Under Settings › Shipping and delivery, look at your saved packages and which one is the store default. Shopify uses the default package "to determine the shipping rate to charge your customers during checkout", and adds its weight to the order.

If your product weights already include packaging, Shopify says "To base rates on product weight alone, set the weight of your default package to zero." Otherwise you count the box twice.
If your weights are for the bare item, keep a realistic box weight on the default package.

Shopify can also choose among your saved boxes for multi-item orders when products have packed dimensions. How automatic package selection works.

Other things that make rates look wrong

A unit mix-up: a weight typed in grams while the unit is set to pounds (or the other way round) makes items hundreds of times too heavy or too light. The CSV column is always in grams. Weight unit for display only changes how the weight is shown.
Requires shipping is off on a physical product, so it doesn't count toward shipping at all.
Rate tiers with gaps, for example nothing set between 5 kg and 10 kg.
Dimensional weight: carriers bill large, light boxes by size, so the label can cost more than the scale weight suggests. The weight helper has a dimensional weight calculator.

Check that it worked

Export again and re-run the checker until "Missing weight" shows 0. Then add a few typical carts in your store, including your heaviest product, and compare the rate at checkout with what the label actually costs.