Carry-On Compliance Checker
Use this tool to see whether your backpack fits airline carry-on size limits. Select a popular backpack or enter custom dimensions to compare against major U.S. and international airlines.
How This Checker Works
This tool compares a backpack’s external dimensions against the published carry-on size limits for 25+ airlines simultaneously. You can either pick a popular travel backpack from the dropdown or enter custom dimensions in inches or centimeters. The result for each airline is one of three states: Fits means every dimension is at or below the published limit; Borderline means within 0.5 in (1.3 cm) of any limit on at least one axis, usually fine but enforcement-dependent; Too large means the bag exceeds the limit on at least one axis.
The published limit is what the carrier states on their website. Real-world enforcement varies, and the sections below explain why a Borderline result on Ryanair behaves very differently from a Borderline result on Delta.
Why Airline Size Limits Are Not Enforced Uniformly
Two airlines can post the same 22 x 14 x 9 inch carry-on allowance and treat your bag completely differently at the gate. The reason is revenue model, not policy. Airlines that earn meaningful income from baggage fees (Ryanair, Frontier, Wizz Air, EasyJet) staff their gates with metal sizing frames and enforce strictly because every oversize bag is direct revenue. Legacy carriers like Delta, United, American, British Airways, and Lufthansa treat carry-on as a service amenity and rarely measure unless a bag is obviously oversize or the flight is full.
A practical consequence: a bag rated Borderline by this checker is a non-issue on Delta, a coin flip on JetBlue, and an automatic fee on Ryanair. Use the airline’s enforcement profile, not just the dimensional result. Every airline guide on this site includes an enforcement assessment based on aggregated traveler reports.
How to Measure a Backpack Accurately
Manufacturer-published dimensions are routinely 0.3 to 0.8 inches smaller than the bag’s actual external size when packed. To measure accurately, pack the bag as you would for a real trip, since most bags expand 0.5 to 1.0 inches when full. Place the bag upright on a hard floor against a wall. Measure from the floor to the highest point including any handle stub or top compression strap. Measure width at the widest external point including side pockets bulging out. Measure depth front-to-back at the deepest packed point, which is where soft-sided bags fail size frames.
For roller bags, the wheel housing counts. For backpacks with external water bottle pockets, a stuffed bottle counts toward depth. Sizing frames do not care about your manufacturer’s tape-measure conventions.
What Size Limits Look Like by Airline Tier
| Tier | Example Carriers | Carry-On (in / cm) | Personal Item | Enforcement |
|---|---|---|---|---|
| Strict EU budget | Ryanair, Wizz Air, EasyJet | 21.6 x 15.7 x 7.9 / 55 x 40 x 20 (priority only) | 15.7 x 11.8 x 7.9 / 40 x 30 x 20 | Metal sizer at every gate |
| Strict US ULCC | Frontier | 22 x 18 x 10 / 56 x 46 x 25 (paid) | 18 x 14 x 8 / 45 x 35 x 20 | Sizer used routinely |
| Major US legacy | Delta, United, American | 22 x 14 x 9 / 56 x 36 x 23 | Under-seat, no published size | Rarely measured |
| Premium international | Lufthansa, Air France, BA | 21.6 x 15.7 x 9 / 55 x 40 x 23 | Yes, with weight cap | Inconsistent |
| Asian / Middle East | Singapore, Emirates, Qatar | 22 x 14 x 9 / 56 x 36 x 23 + 7-10 kg cap | Yes, with weight cap | Weight is the real test |
The dimensional limit is only half the rule on European, Asian, and Middle Eastern carriers, which also enforce a weight cap (typically 7 to 10 kg / 15 to 22 lb). The checker reports dimensions only. Verify the airline’s weight cap separately if you fly internationally. The complete size limits guide covers both dimensions and weight caps for every airline.
What “Personal Item” Really Means
The personal item allowance is the most under-communicated part of carry-on policy. On strict budget carriers, the personal item is your free bag and the carry-on costs extra. On Ryanair, only a 40 x 30 x 20 cm bag flies free; an actual carry-on requires Priority boarding. On Frontier, an 18 x 14 x 8 inch personal item flies free; a paid carry-on adds a significant surcharge depending on when you add it.
A 35-liter backpack like the Cotopaxi Allpa fits the strict-EU personal-item slot only if compressed. A 40-liter Osprey Farpoint or Tortuga Pro will not fit a strict personal-item box regardless of how it is packed. Use the checker’s Personal item mode (toggle in the widget) to test against the smaller limit.
What Gate Agents Actually Check
Three signals trigger a gate measurement: the bag visibly overhangs the boarding-pass scanner stand; the flight is full and the agent is preempting overhead-bin shortages; or the airline’s policy is to size 100% of bags (Ryanair, EasyJet, Frontier). On legacy US carriers, fewer than 5% of bags get measured on a typical flight. On Ryanair, 100% do.
Soft-sided backpacks have an asymmetric advantage at gate sizers. A hard-shell roller that is 0.4 inches too long fails. A backpack 0.4 inches too tall typically slides into the frame because the top compresses. This is why the bag picks on this site lean heavily toward soft-sided travel backpacks despite roller bags being more popular in airport lounges.
Frequently Asked Questions
Why does this tool say my bag fits Ryanair when Ryanair’s website says it doesn’t?
The dimensional check passes, but you also need Priority boarding to bring a carry-on at all on Ryanair. Without Priority, only the 40 x 30 x 20 cm personal-item bag is free. Add Priority when booking to use the larger 55 x 40 x 20 cm allowance.
How accurate are manufacturer dimensions?
Generally optimistic by 0.3 to 0.8 inches when the bag is packed. We note measured differences where possible. For new bags we have not measured, treat the dimensional result as “fits” only if the bag is at least 0.5 inches under the limit on every axis.
Does this tool track airline policy changes?
Policy data is reviewed monthly against each carrier’s official baggage page and updated when changes are detected. The last review date appears in the page footer. If you spot a discrepancy, please report it via the contact page.
What about checked-bag rules?
This tool only covers carry-on and personal-item allowances. Checked-bag dimensions, weight limits, and fees vary far more and are not in scope.
Is the Big Front Seat carry-on rule different on Spirit?
Spirit ceased operations in May 2026. Before the shutdown, Big Front Seat passengers received the same personal item allowance as economy passengers. The carry-on bag was a paid add-on at the same price tiers regardless of seat class.
Last updated: August 2026