How do I check whether my suitcase fits an airline's cabin-bag rules?

Compare the suitcase’s complete outside dimensions—height, width and depth—with the current allowance for your booked flight. Include wheels and handles. For example, American Airlines says its carry-on must fit its airport sizer and must not exceed 22 × 14 × 9 inches, including handles and wheels. It also notes that some airports and planes may have additional restrictions. That is one airline’s rule, not a universal limit. [S1]

Check the airline operating each flight, your booked fare’s allowance and the itinerary details. If your journey includes a partner-operated flight, check that segment too: codeshare partners can have different rules. [S2]

Use a tape measure and write down three outside measurements: height, width and depth. Measure to the furthest point in each direction, including wheels, handles and rigid parts that affect the bag’s overall size. Keep the units consistent with the airline’s published limit, or convert before comparing.

Compare each measurement separately with its corresponding maximum. Don’t assume that being under a combined total means the bag passes: individual dimension limits and a combined linear limit are different measures. Delta lists dimensions up to 22 × 14 × 9 inches, including handles and wheels, as well as a 45-linear-inch combined maximum. [S2] Apply the rule for your flight, rather than substituting one measurement method for another.

Here’s a copyable worksheet. Your measurements are from your example; the allowance and result are not confirmed until you check your itinerary.

Cabin-bag comparison

1. Operating airline for each segment: [airline]
2. Booked flight and fare: [flight details] / [fare]
3. Current cabin-bag allowance for this booking: [dimensions and any other stated limit]
4. Suitcase dimensions, including wheels and handles: 21 × 14 × 9 inches
5. Height: 21 inches compared with [height limit]
6. Width: 14 inches compared with [width limit]
7. Depth: 9 inches compared with [depth limit]
8. Partner-operated segment or unusual aircraft to confirm: [details]
9. Result: [within published limits / exceeds a limit / needs airline confirmation]

If the applicable limit happened to be 22 × 14 × 9 inches, your example dimensions would be at the limit for width and depth. That comparison alone does not establish the allowance for your unconfirmed itinerary. American and Delta publish those dimensions for their respective rules, not as a universal limit. [S1][S2]

No. Treat the size check as one part of the decision. American notes that some airports and planes may have additional carry-on restrictions. Delta says some Delta Connection flights have limited cabin space and bags may be gate-checked; it also notes that codeshare partners can have different rules. [S1][S2]

Check the itinerary’s current allowance and ask the carrier about any partner-operated segment or unusual aircraft. A size comparison cannot guarantee that a bag will remain in the cabin. The supplied airline information does not establish the rule or outcome for your particular booking.

Contact the airline using the options provided with your booking or on its official site. Give the flight number, operating airline for each segment, fare and your suitcase’s full measured dimensions. Ask which allowance applies to each segment and whether there is any aircraft- or partner-specific detail to confirm. Note the answer and when you checked it; recheck current information if your itinerary changes.

You could ask:

“Please confirm the current cabin-bag allowance for my booked itinerary: [flight numbers], operated by [airline(s)], on fare [fare]. My suitcase measures [height] × [width] × [depth], including wheels and handles. Does it meet the allowance for each segment, and is there any aircraft- or partner-specific detail I should confirm?”