How to measure correctly
- Stand the bag upright.Measure from the floor, including wheels, to the highest part of the handle housing.
- Measure the widest point.Include side handles, feet and any bulge from a fully packed compartment.
- Measure depth when packed.Expansion zips and front pockets can turn a compliant bag into an oversized one.
- Weigh the complete cabin load.Some airlines combine a personal item with the main cabin-bag weight.
Why a “55 cm cabin bag” can still fail
Retailers often lead with one dimension. IndiGo and SpiceJet Boeing flights publish 55 × 35 × 25 cm, while Air India publishes 55 × 40 × 20 cm. The same trolley can fit one envelope but exceed another because it is too deep.
Strictest-leg rule
If your itinerary uses more than one airline—or a SpiceJet Q400—pack for the smallest applicable allowance.