Photo by Rob Speed

Unlike other U.S. airlines, Southwest does not stipulate what size carrier it will accept for in-cabin pets. Instead, it has published the dimensions of the under-seat space available to travelers. Southwest has a fleet of Boeing 737s (the -300, -500 and -700 series), and apparently the same measurement applies to all of its planes.

Southwest’s under-seat dimensions are as follows:

• Window Seat: 19″L x 14″W x 8.25″H
• Middle Seat: 19″L x 19″W x 8.25″H
• Aisle Seat: 19″L x 14″W x 8.25″H

I think this is a very sensible approach. You can look at these dimensions and really understand that an in-cabin carrier that’s 20″ long just won’t fit. You can test, at home, whether your carrier can flex enough to fit under an 8.25″ ceiling and still give your pet the headroom she needs. I hope more airlines follow Southwest’s lead!

A few months later I traveled on a Southwest 737 (-700 series) with a tape measure, and posted a follow-up message about choosing seats with an in-cabin dog on Southwest.