Alaska Airlines is moving ahead with plans to expand long-haul flying from Seattle-Tacoma International Airport (SEA) with an ...

The general rule is that it must fit under your seat or in the overhead enclosed storage compartment on the plane. Here's a quick reference for size limits for the most popular US airlines.

United Airlines: United limits underseat luggage to 9 by 10 by 17 inches. Southwest Airlines: Personal items must fit in the 16.25- by 13.5- by 8-inch space underneath the seat in front of you.