One folding chair quoted a Purolator rate at checkout. Two folding chairs quoted nothing. Same chair, same address, same store. The only thing that changed was the quantity.
The cause is a Shopify behaviour that isn’t documented anywhere near where you’d look for it: a package you assign to a product only applies to single-item orders. The second a cart holds two or more items, Shopify discards that assignment and packs the whole order into your store default package. If that default box is the wrong size, every multi-item order quietly loses its carrier rate, and nothing in the admin tells you why.
This is a sequel to the last shipping post I wrote, from the same office furniture build. Different failure, same theme: Shopify’s shipping behaviour and Shopify’s shipping documentation have drifted apart.
What the symptom looks like
The store sells everything from $40 desk lamps to 215 lb executive desks. Purolator handles the parcel-size items. A custom Cloudflare Worker handles the freight, the heavy stuff that ships LTL on a pallet through Manitoulin Transport.
I noticed the bug on chairs, then went looking for the pattern by testing a small product and a large one. The pattern held on both. One unit of anything: Purolator quotes. Two units of anything: Purolator disappears from checkout. No error. No “shipping not available for this carrier” line. The rate is just gone.
So this isn’t a chair problem, and it isn’t a Purolator problem. It’s every product in the store, the moment the cart count hits two.
Why does Shopify drop the rate when there’s more than one item?
Here’s the part the docs bury. In Shopify you can assign a specific package (a box with real dimensions) to a product or variant. That assignment overrides your store default package when Shopify calculates a rate. But it overrides the default only for orders that contain a single item.
For any order with multiple items, Shopify ignores the per-product package entirely and calculates the rate using your store default package, as one combined box, for the whole cart.
Read that again, because it explains a class of bugs. You can set perfect dimensions on every product in your catalogue, watch single-item checkouts quote beautifully, and still have every two-item order fail, because two-item orders never touch those product packages. They fall back to one box: the default.
That also means the store default package is not a fallback you set once and forget. It’s the box that does the heavy lifting on the majority of real orders. People order more than one thing.
The store default box was the actual problem
I opened Settings, Shipping and delivery, Packages, and there it was. The store default was a 25 by 28 by 48 inch box. An oversize specialty carton, set as the everyday catch-all.
Run the numbers against Purolator. Their parcel ceiling is 150 lb per piece and a maximum of 165 inches for length plus girth, where girth is twice the width plus twice the height. That default box: 48 length, plus 2 × (25 + 28) girth, equals 154 inches. Eleven inches under the limit.
So one item in that box just barely clears. There’s almost no headroom. Add a second item and Shopify needs more box than 154 inches gives, the package tips past 165, and Purolator declines. Weight was never the issue. The chairs are 8 lb. It was the box, and the fact that a near-maxed box leaves no room for a second anything.
The store default package is the single most important shipping setting in Shopify, and almost nobody sets it on purpose. It gets left on whatever box happened to be selected, and it quietly decides whether your multi-item orders can be shipped at all.
The fix
Three moves, in order of impact.
- Right-size the store default package. Set it to a normal box your typical small order actually goes out in, not an oversize specialty carton. This one change fixes the universal multi-item failure on its own.
- Give every product an accurate weight. Weight is a real field on the product, and it’s what tells Shopify and the carrier whether something is a parcel or freight. Without it, everything leans harder on that default box.
- Split parcel from freight with shipping profiles. Put the heavy items (desks, file cabinets, anything palletized) in their own profile that quotes your freight carrier and does not offer Purolator. Keep the parcel items on the profile that offers Purolator. A 215 lb desk should never show a parcel rate, and a desk lamp should never try to ship LTL.
Then test it the only way that counts. Put two of the same small item in a cart and watch Purolator come back.
Can you make each item ship in its own box?
This is the question I get next, and the honest answer is no, not with Shopify’s built-in shipping.
For multi-item orders, native Shopify uses one package (the store default) and returns one combined rate. It does not box items individually, and it does not request a separate carrier rate per box. If two of your items physically cannot share a carton, the native system has no way to quote them as two parcels.
You have two real options:
- Put them in one right-sized box. If two folding chairs can nest into a single carton that stays under the carrier’s limit, this is the simplest and most reliable fix, and it costs nothing. Most parcel items can share a box.
- Add a packing app for true per-box rates. If items genuinely must ship as separate parcels, a third-party shipping app (Intuitive Shipping, ShipperHQ, and others on the Shopify App Store) can box each item and request a rate per box. That’s the only way to get real per-parcel pricing on a multi-item order.
Start with the box. Reach for the app only when the boxes truly can’t combine. I’ve seen stores carry a paid shipping app for years to solve a problem that was a wrong default-package setting all along.
The setting worth checking on your own store today
If you sell anything customers buy more than one of, open Settings, Shipping and delivery, Packages, and look at what your store default package actually is. Not the boxes you assigned to products. The default.
If it’s an oversize box, or a box nobody chose deliberately, your two-item orders are probably failing right now and you’d never see it from the admin. The customer sees it. They get to checkout, find no shipping option, and leave. That’s a conversion leak with no error message attached to it, which is the worst kind, because nothing tells you it’s happening.
Single-item test orders will keep passing the whole time. So test with two.
Bunker41 is a one-person studio in Sault Ste. Marie, Ontario building custom websites and web apps for small businesses. If your Shopify store is quietly losing shipping rates at checkout and the docs aren’t helping, say hello.