Airlines love to talk about a “standard” carry-on size, but there is no such thing. Every major U.S. carrier sets its own limits, and the gap between the most generous and the strictest is bigger than most travelers realize — sometimes four extra inches in a single dimension. A bag that glides through the gate on Southwest can get flagged on Delta. To settle the question, here’s what each airline’s own baggage policy actually allows for carry-ons and personal items, pulled straight from their official pages.
1. Delta Air Lines
Delta caps carry-ons at 22 x 14 x 9 inches, or 45 linear inches combined, measured including handles and wheels, according to Delta’s own carry-on baggage page. Personal items — a purse, laptop bag, or small backpack — just need to fit under the seat in front of you; Delta doesn’t publish exact dimensions for that bag. There’s no stated weight limit for either item, only that you’re able to lift it into the bin yourself.
2. American Airlines
American allows the same 22 x 14 x 9 inches for carry-ons, per American’s official baggage policy, and it gets more specific on personal items: 18 x 14 x 8 inches, covering things like a backpack or duffel bag. No weight limit applies to either bag on most flights, though American Eagle regional jets sometimes route oversized carry-ons to gate-check through a valet service instead of the overhead bin.
3. United Airlines
United also holds the line at 22 x 14 x 9 inches for carry-ons, with personal items capped at 17 x 10 x 9 inches, according to United’s carry-on bag policy. That personal-item allowance runs a notch smaller than what Delta or American effectively permits, so a bag that clears one airline’s underseat check can still get stopped at United’s gate.
4. JetBlue
JetBlue sticks to the same 22 x 14 x 9-inch carry-on standard, but its personal item is the most generous of the group at 17 x 13 x 8 inches, per JetBlue’s baggage guidelines. Neither bag carries a published weight cap, though JetBlue notes passengers should be able to lift their own carry-on into the overhead bin unassisted.
5. Alaska Airlines
Alaska keeps carry-ons at the familiar 22 x 14 x 9 inches, according to Alaska’s carry-on baggage page, and it’s one of the few carriers that doesn’t enforce a strict weight limit on that bag at all, as long as you can lift and stow it yourself. Alaska doesn’t publish firm personal-item dimensions, only that it must fit under the seat, leaving more room for interpretation than most rivals allow.
6. Southwest Airlines
Southwest is where the size limits jump. Its carry-on allowance is 24 x 16 x 10 inches — noticeably bigger in every dimension than Delta, American, United, JetBlue, or Alaska — according to Southwest’s carryon baggage policy. A bag packed to Southwest’s limit could get rejected at a Delta or United gate for being too tall, too wide, and too deep all at once. Personal items just need to fit under the seat, with no fixed dimensions published.
7. Spirit Airlines
Spirit allows a carry-on up to 22 x 18 x 10 inches — four inches deeper than the Delta, American, and United standard — with personal items capped at 18 x 14 x 8 inches. Spirit is also the airline where sizing hits your wallet hardest: unlike most competitors, it charges a separate fee for any bag placed in the overhead bin unless that fee is already folded into a bundled fare.
8. Frontier Airlines
Frontier matches Southwest’s roomier 24 x 16 x 10-inch carry-on allowance and its 18 x 14 x 8-inch personal item, according to Frontier’s bag options page. It’s also the only carrier on this list to publish a hard weight limit — 35 pounds — on both the carry-on and the personal item, so a bag that’s oversized but light could clear one test and still fail another.
Line them up and a pattern appears: five airlines — Delta, American, United, JetBlue, and Alaska — enforce the same tight 22 x 14 x 9-inch ceiling, while Southwest and Frontier allow a noticeably roomier 24 x 16 x 10 inches, and Spirit splits the difference with extra depth instead of extra height. The real risk isn’t packing too big for one flight — it’s packing to your usual airline’s rules and assuming the next one plays by the same ones.
