Airline bag sizers explained
A gate sizer is a three-dimensional pass-or-fail test. Your packed bag must fit inside the box without an outside wheel, handle or pocket crossing the frame. The three side limits matter individually; a favourable total in centimetres or linear inches does not usually compensate for one edge that is too long.
The geometry in plain English
Imagine a bag measuring 54 × 39 × 22 cm and a sizer measuring55 × 40 × 23 cm. Match longest to longest, middle to middle and shortest to shortest. The clearances are 1 cm, 1 cm and 1 cm, so it fits by size.
Turning the bag is allowed by the geometry because the labels “height”, “width” and “depth” change with orientation. What cannot change is the set of three outside edge lengths. This is the same orientation-independent comparison used by the FitsOnBoard checker.
Why linear size can give the wrong answer
Two bags can have the same total dimensions but very different shapes. A 60 × 30 × 20 cm bag and a 55 × 35 × 20 cm bag both add up to 110 cm. Against a 55 × 40 × 20 cm sizer, the second bag fits exactly while the first is 5 cm too long. Add the sides only where the carrier expressly uses a linear-total rule, as Singapore Airlines does for its main cabin piece.
What common bag sizes unlock
The table uses the 52 manually maintained airline profiles currently eligible for search. “Fits” includes an exact dimensional match; fare and weight still need a separate check.
| Packed bag size | Typical use | Fits free | Fits paid/upgrade |
|---|---|---|---|
| 40 × 30 × 20 cm | common European under-seat bag | 51/52 | 1/52 |
| 45 × 35 × 20 cm | larger under-seat / US personal item | 43/52 | 9/52 |
| 55 × 40 × 20 cm | slim European cabin trolley | 21/52 | 11/52 |
| 55 × 40 × 23 cm | standard European cabin trolley | 19/52 | 8/52 |
Dataset snapshot: 7 September 2026. A route, fare or operating carrier can change the entitlement; the linked airline profile explains those exceptions and links to the official policy.
This table uses the smaller set of profiles with full public airline guides. For the broader result, see our 151-airline carry-on size study →
What a sizer result does not tell you
- 1Fare: a bag may fit the large box but not be included with your ticket.
- 2Weight: dimensions can pass while a 7, 8, 10 or combined limit fails.
- 3Space: a compliant overhead bag can be moved to the hold on a full flight.
- 4Contents: liquids, batteries and prohibited items follow separate security rules.
Run your own sizer test
Use the packed outside measurements. Add weight if you know it, then open an airline result to review the fare-specific explanation.
Check your bag
Enter your bag’s three dimensions to see which airlines it fits.
Bag sizer FAQ
Can I turn my bag sideways in an airline sizer?+
Yes, a rectangular bag can normally be rotated to match the sizer. Rotation cannot solve an oversized edge: after sorting both sets of dimensions, each bag edge still needs to be no larger than its matching box edge.
Is total linear size enough to know if a cabin bag fits?+
Usually not. A 60 × 30 × 20 cm bag and a 55 × 35 × 20 cm bag both total 110 cm, but the first fails any sizer with a 55 cm longest side. Use total size only when an airline explicitly publishes a linear-sum rule.
Can a soft bag be squeezed into the sizer?+
A soft bag may compress if it is not overpacked, but the outcome depends on its frame and contents. Measure it packed and leave margin instead of planning to force it into the box.
Does passing the sizer guarantee the bag stays in the cabin?+
No. A dimensionally compliant overhead bag may still be gate-checked when locker space is limited, and it must also meet fare, piece-count, weight and restricted-item rules.