A carry-on claim is only true against a named airline’s limit on a given date. So publish the numbers behind it: the bag’s external dimensions in centimetres and inches, labelled height, width and depth; whether they were measured empty or packed, and with handles and straps included; its capacity and how you measured it; and the airline limits you actually checked, with the date you checked them.
In our October 26, 2026 snapshot of Shopify’s agent catalog, ten anti-theft backpacks came back for a city-travel search. Two descriptions said “carry-on compliant”. None named an airline. On its listed dimensions, that bag is within three major airlines’ standard carry-on limits and over two of their personal-item limits. On paper, “compliant” held for one kind of allowance and not the other.
The fact card below is a proposed record, not a format any platform requires.
What ten backpack listings said
On October 26 we searched Shopify’s Global Catalog, the product catalog Shopify makes available to AI shopping channels, for “anti theft backpack for city travel”. All ten results share one maker: eight sold by that maker’s own store, two by a reseller. (Counting products and sellers separately is its own subject; see our seller-concentration count.) Store names are withheld; listings go by position.
“Generated” means the specification list Shopify writes and marks Inferred, not the merchant’s description.
| Position | Seller | Capacity stated | Dimensions stated |
|---|---|---|---|
| 1 | Maker’s store | 17 L | 15.4 x 10.6 x 6.3 in (generated) |
| 2 | Maker’s store | 35 L | 12.2 x 7.9 x 20.5 in (generated) |
| 3 | Maker’s store | 25 L | 48 x 31 x 18 cm (generated) |
| 4 | Maker’s store | 26 L (1587 cu in) | 18.3 x 11.4 x 7.8 in (generated) |
| 5 | Maker’s store | 28 L | 19.7 x 11.2 x 7.5 in (generated) |
| 6 | Maker’s store | 20 L | 44.96 x 27.94 x 6.86 cm (generated) |
| 7 | Maker’s store | Not stated | 13.4 x 10.2 x 4.7 in (generated) |
| 8 | Reseller | 28 L | “Height: 11.2 inch Width: 7.5 inch Depth: 2.4lbs” (description) |
| 9 | Maker’s store | 16 L (976 cu in) | 16.1 x 11.4 x 5.1 in (generated) |
| 10 | Reseller | 25 L | 18.9 x 12.2 x 7.1 in (description); 20 L and 25 L sizes (generated) |
Here’s what’s there and what isn’t:
- Capacity: stated in some field on 9 of 10. Not one record said how it was measured, or whether pockets were counted.
- Dimensions: on all 10, but in the merchant’s own description on only 2. The other eight rely on Shopify’s generated list.
- Which number is which: only position 8 labelled height, width and depth, and that’s the record with a weight in the depth slot. The others are bare triples, in different orders. Position 2 puts the largest number last; most put it first.
- Empty or packed: not stated on any record.
- Airline: not named on any record. Two descriptions said “carry-on compliant”; Shopify’s generated selling points turned one of those into “travel-compliant design”.
Every number a shopper needs to check carry-on fit is nearly there. What’s missing is the context that would let anyone check it: which side is which, in what state, against whose limit.
Worked example: the “carry-on compliant” 25-litre bag
Positions 3 and 10 appear to be the same 25-litre bag, sold by the maker’s store and by a reseller. Their records agree once you convert units. Position 3’s generated 48 x 31 x 18 cm is 18.9 x 12.2 x 7.1 in, which is what position 10’s description says. Position 3’s 1 kg matches position 10’s 2.2 lbs. Consistent data, which makes it a fair test of the claim itself.
Here it is against three airlines’ published limits, as we read them on October 27, 2026. The airlines list their sides in different orders, so we compared largest side with largest limit.
| Limit (checked Oct 27, 2026) | Maximum size, largest first | The 48 x 31 x 18 cm bag | Result on paper |
|---|---|---|---|
| Air Canada standard carry-on | 55 x 40 x 23 cm | All three sides within | Fits |
| Air Canada personal item | 43 x 33 x 16 cm | 48 > 43 and 18 > 16 | Over |
| United carry-on | 56 x 35 x 23 cm | All three sides within | Fits |
| United personal item | 43 x 25 x 22 cm | 48 > 43 and 31 > 25 | Over |
| Delta carry-on | 56 x 35 x 23 cm; 114 cm combined | Within; 97 cm combined | Fits |
| Delta personal item | No dimensions on its carry-on page | — | Unknown |
So “carry-on compliant” holds, on paper, for the standard carry-on allowance at all three. As a bag that goes under the seat, it’s over the published limit at the two airlines that publish one. Fares matter too. Air Canada says some Economy Basic fares bought on or after January 3, 2025 allow only a personal item on some itineraries. United says you get a carry-on and a personal item if you’re not in Basic Economy. A traveller on one of those fares, carrying only this bag, is relying on the personal-item limit, and the listing never tells them that.
Three conditions could still change the result, and the listing answers none of them:
- Do the dimensions include the straps and handles? All three airlines measure with handles and wheels included.
- Were they measured empty or packed? A soft bag packed full can be thicker than its empty measurement.
- Which side is the depth? 18 cm against a 23 cm limit is fine. If the 31 cm side were the depth, it wouldn’t be, so label the sides.
That’s the gap between airline-friendly copy and a fit claim someone can check.
A wrong depth can make a bag look like a personal item
Positions 5 and 8 appear to be the same 28-litre bag, from the maker’s store and a reseller. Position 5’s generated list gives 19.7 x 11.2 x 7.5 in. Position 8’s description says “Height: 11.2 inch Width: 7.5 inch Depth: 2.4lbs”, and Shopify’s generated list turned that into “Depth 2.4 in”. Both records give the weight as 2.4 lbs. (Both records are quoted here.)
It looks as if the weight slid into the depth line, and the height dropped out. We can’t prove that, and we didn’t check either figure against the manufacturer. But look at what each record implies:
| Record | Dimensions | Fits Air Canada / United personal item? | Box volume vs stated 28 L |
|---|---|---|---|
| Position 5 | 19.7 x 11.2 x 7.5 in (50.0 x 28.4 x 19.1 cm) | No, longest side over 43 cm | About 27.1 L: plausible |
| Position 8, read at face value | 11.2 x 7.5 x 2.4 in (28.4 x 19.1 x 6.1 cm) | Yes, on both | About 3.3 L: impossible for 28 L |
A careless checker, human or software, reading position 8 would conclude this 28-litre backpack slides under a seat. The volume check catches it in one line of arithmetic. A soft bag isn’t a box, so this is a rough test. But external dimensions that multiply out to a tenth of the stated capacity mean a number is wrong.
Units are part of the problem. “Depth: 2.4lbs” puts a weight unit on a length, and the generated list quietly changed the unit to inches instead of flagging it. For how units get normalized, and mangled, between a listing and a shopper, see our unit normalization research.
The capacity and fit fact card
One card per variant. If a product comes in two sizes, it needs two cards. Position 10’s generated list put a 20 L and a 25 L size’s dimensions in one record, which is exactly how a shopper ends up with the wrong size’s numbers.
| Field | What goes in it | Format |
|---|---|---|
| Variant | The exact size and colour the card describes | 25 L, black |
| Capacity | Litres, plus cubic inches if you sell in the US | [ ] L ([ ] cu in) |
| Capacity method | What was counted (main compartment, pockets, expansion) and how | [Main compartment and pockets, filled with [ ], measured by [ ]] |
| External dimensions | Labelled: height x width x depth, cm and in | H [ ] x W [ ] x D [ ] cm ([ ] in) |
| What’s included | Handles, straps, feet, wheels: in or out of the measurement | [Includes top handle; excludes shoulder straps] |
| Measured state | Empty, packed to capacity, or expanded | [Empty / packed / expanded] |
| Weight | Empty weight, kg and lb | [ ] kg ([ ] lb) |
| Laptop sleeve | Internal sleeve dimensions, or the laptop models you tested | [ ] x [ ] cm; fits [model] |
| Limits checked | Airline, allowance type, its limit, date checked | [Airline] carry-on, [limit], checked [date] |
| Doesn’t fit | Allowances it exceeds, with the side that’s over | [Airline] personal item: height over by [ ] cm |
| Source and checked | Spec sheet or your own measurement, and the date | [Document or “measured by us”], [date] |
The brackets are deliberate. Fill them from the factory spec sheet or by measuring the bag yourself, and write “not measured” rather than leaving a gap.
The 25-litre bag, carded from what the catalog returned
| Field | What the two records said | Status |
|---|---|---|
| Capacity | 25 L in titles and descriptions | Stated; method unknown |
| External dimensions | 48 x 31 x 18 cm and 18.9 x 12.2 x 7.1 in, sides unlabelled | Stated; agree; axes unknown |
| What’s included / measured state | Not stated | Unknown |
| Weight | 1 kg and 2.2 lbs | Stated; agree |
| Laptop sleeve | Position 10: “Fits a 15” laptop”; position 3: “fleece-lined laptop sleeve”, no size | Partial |
| Limits checked | “Carry-on compliant”, no airline or date | Claim with no comparison |
| Doesn’t fit | Not stated | Missing: over two personal-item limits by our arithmetic |
Three rows (labelled sides, measured state, sleeve size) can be fixed with a tape measure and ten minutes. The last two need the airline pages and a date. Replace “carry-on compliant” with the comparison itself: “Within Air Canada, United and Delta standard carry-on limits; over Air Canada and United personal-item limits (checked October 27, 2026)”. Then recheck it on a schedule, because airline rules change and your claim changes with them.
How an agent or shopper will check your listing
This is the evaluation a careful agent, or a careful traveller, can run on a travel-bag listing. Run it first.
| Shopper question | Evidence that answers it | Trap to avoid | When the bag should be ruled out |
|---|---|---|---|
| Will it fit as my carry-on on this airline? | Labelled external dimensions, handles included, packed state, the airline’s current limit | “Carry-on compliant” with no airline | Any side over that airline’s carry-on limit |
| Will it go under the seat? | The same dimensions against a personal-item limit | A bag that meets carry-on limits sold as if it meets personal-item limits | Any side over the personal-item limit, or a fare that allows only a personal item |
| How much does it hold? | Litres, with the method | Capacity that includes an expansion zip or pockets without saying so | Stated capacity below the shopper’s need |
| Does my laptop fit? | Internal sleeve size or tested models | “Laptop sleeve” with no size | Laptop larger than the sleeve |
| Are the numbers believable? | Box volume close to stated capacity; one set of units per field | A weight unit on a length; two sizes in one record | Dimensions that can’t hold the stated capacity |
The last column protects you as much as the shopper. A bag pulled off a plane at the gate turns into a return and a bad review. A true “over the personal-item limit” line costs you only the buyers it was never going to suit.
Shopify says its generated fields, including specifications and selling points, can vary in accuracy and aren’t merchant-authored text. OpenAI says ChatGPT may write simplified product descriptions and that its feature labels aren’t guarantees. Either way, the safest fit claim is a set of numbers in your own fields that anyone can check. Shopify’s Catalog Mapping can pull data from custom fields such as metafields, so put the fact card in structured fields as well as in visible text. The field-by-field format behind this card is in our product specification template. The same approach for pet gear is in pet gear data.
How we checked
- Source: Shopify’s public Global Catalog, searched read-only on October 26, 2026 through Shopify’s official UCP command-line tool. No buyer context, no country, top 10 results.
- Query: “anti theft backpack for city travel”, exactly as written.
- What we read: for each result, the title, the description, the options, the first variant’s seller and options, and Shopify’s generated specification, feature and selling-point lists. The response carried one variant per product.
- How we counted: case-insensitive text matching for capacity (litres), dimension triples, height, width and depth labels, weight, airline terms (airline, personal item, under seat, overhead), loaded-state terms (packed, empty, loaded, expand) and measurement-method terms. We then read all ten records by hand on October 27 to confirm each match and its field.
- Airline limits: read from the Air Canada, United and Delta carry-on pages on October 27, 2026. Comparisons are our arithmetic on seller-listed dimensions, largest side against largest limit, with 1 in = 2.54 cm.
- What we didn’t do: measure any bag, use a sizer, or open product pages and manuals.
What the evidence supports, and what it doesn’t
The snapshot supports a narrow claim: on one search, on one day, in one catalog, the “carry-on compliant” bag’s records carried consistent dimensions but no airline, no labelled sides and no packed state, and a second bag’s records carried a weight where a depth should be. It doesn’t show how common that is across travel bags, or what ChatGPT or any other assistant told anyone.
The airline pages support a dated comparison, not a permanent one. They also show why a single “carry-on” word can’t be universal: three airlines, carry-on limits that differ by a few centimetres plus one combined-size rule, two published personal-item limits and fare rules that change which one applies.
Your next step
Take your best-selling bag and a tape measure. Measure height, width and depth with the handles in, once empty and once packed. Write both on the fact card in centimetres and inches, labelled. Then open the carry-on pages of the two airlines your customers fly most, compare both allowances, and replace “carry-on friendly” with the comparison and today’s date.