Returning to Seattle from a week in North Carolina (which explains why things have been so quiet on the blog recently), I flew for the first time on one of Southwest’s new 737-800 planes — so new, in fact, that it smelled like new plane, which is just as pleasing as new car. You’ll like them, when you get on one — the top half of the bulkhead between the first row and the flight attendants is gone, and in general the plane feels wider and more open; the overhead baggage compartments hold more stuff and are easier to close; and the flight attendant call button is located far, far away from the reading light buttons.

Anyway, it’s a new plane to me, so I grabbed my tape measure and threw myself on the ground. Here’s what I learned. As on other Southwest planes, the depth of the under-seat space (measured from the rail just behind the heels of the person in front of you to the nearest end of the bracket supporting the seat in front of you) is 17″. There are packets under each seat holding a life jacket, but they are soft, and can be pressed upwards — the under-seat height, therefore, is 11.5″ to 12″. The aisle seats have one of those pesky bars running around the under-seat space, reducing the available width to 14.25″, but the middle seat space is a generous 20″ wide, and the window seat space is a very respectable 18.5″ wide.

If you compare these measurements to Southwest’s 737-700 measurements, you’ll see that the middle and window under-seat spaces on the -800 series have more left-to-right room, and the change from a hard to soft enclosure for the life jackets means that all of the under-seat spaces are effectively 2-3″ taller. If you walk on a Southwest plane and can see the first port-side row from the door, start smiling — you’re on a 737-800, and your pet’s carrier will fit way more easily under your seat than you’re used to.

This post is part of an ongoing series recording under-seat measurements of the various planes we fly on. Keep in mind that most domestic and international airlines have rules about the maximum size of in-cabin pet carriers they allow on board (see Dog Jaunt’s handy charts under the “Taking your pet on a plane” tab above).