Alaska Airlines is reducing the size limit for carry-on luggage in an effort to match the industry standard and prevent bag size conflicts for travelers on connecting flights.
Beginning June 4, 2018, the size limit for Alaska Airlines, Horizon and SkyWest flights will change to 22'' x 14'' x 9''. Currently, the maximum dimensions for carry-on luggage are 24" x 17" x 10".

Passengers will still be allowed one carry-on bag and one personal item.

The airline said it's shrinking the dimensions to be consistent with most other carriers so that passengers won't be surprised when they have to check their carry-on luggage on another flight.
The reduced dimensions will also allow more carry-on bags to be stored in the overhead bins.
To help ensure a smooth transition, Alaska Airlines will add updated bag sizers at various airport locations in the coming months, allowing customers to measure their bag dimensions beforehand.

The new size limit will mirror those of American Airlines, Delta Air Lines, and United Airlines. Meanwhile, Southwest Airlines' limit of 24" x 16" x 10" will become the largest among major U.S. carriers.