In case you need a reminder that different airlines configure a plane differently, here’s another A320 to tell you about. We flew on a United A320 today, and on this plane, your best choices with an in-cabin dog are an aisle or middle seat.

The cabin is divided into three classes: First, Economy Plus and Economy. First Class has two seats on each side of the aisle; the rest of the plane has three seats on each side of the aisle. Economy Plus has five more inches of leg room, and if you can, I urge you to choose Economy Plus. Reaching down to pat your dog or give her ice cubes during the flight is way, way more comfortable with the extra space.

There is a bulkhead in front of Row 1, in First Class, and in front of Row 6, in Economy Plus. You can’t have an in-cabin dog if you’re sitting in Row 1, and although there is a big cut-out in the bulkhead in front of Row 6, only service dogs are allowed in that row.

The under-seat space in Economy Plus and Economy is the same in all rows. The seats support a life vest packet, but it’s in a soft package, so it presses up against the seat bottom. That gives you 10 inches of height under all the seats. The aisle seats are 18 inches wide, the middle seats are 19.5 inches wide, and the window seats are 17 inches wide. Measured front to back, the under-seat space is about 17 inches deep.

I only caught a couple of fleeting glimpses of the First Class seats — someone traveling First Class will have to post a comment with measurements! — but the First Class under-seat space is also divided into three sections. The largest, middle section is hopeless — it’s almost entirely occupied by an enormous electronics box. The space closest to the window, however, looked pretty promising. The space closest to the aisle looked very narrow. If you plan to travel First Class with an in-cabin dog on a United A320, go for a window seat.

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).