I think you'll be fine. The very fact that you are conscious of it means that you will be respectful of your neighbor's space. I'm small only mention because it isn't as if I am in their space) and I've sat next to thin men and women and they have invaded my space way more than larger than what we think of as average women have. The worst actually is men over 30 that are tall - they seem to think they own the row.

If you're short and wear a 20 it might be very tight. Airlines are far more accommodating to customers of size than to the people sitting next to them.

If there is space on the some airlines' attendants move people around even bumping up those who are in premium seats to first class moving COS to aisles and no middle seat passenger.

If you're on SW get priority boarding and no one will sit with you.

You'll be fine!

At size 20 you definitely should not need an extra seat, but maybe a belt extender depending on how you carry your weight. I range from an 18 to 20 and have never felt like I needed either, but I will put up the arm rest between my 3 yo and myself for extra room.

Have you considered just getting a first class seat? On a lot of domestic flights the first class upgrade isn't that expensive. I don't think you need it, but if it reduces your anxiety and allows you to travel it might be worth it.

At the point where you need to wedge yourself in the seat and still spill over onto your neighbour, thats when you need an extra seat. But for that, you need to be much bigger than you are, OP.

As an example, my MIL is over 300 pounds and should really have 2 seats but my FIL is quite slender so between the two of them, they fit.

Several years ago I was a size 16 (as in size 16 was just slightly too tight on me but I could fit in it) and I didn't need 2 seats or even a seat belt extender.
I know weight distribution can vary by person, but I think it's very unlikely you will need two seats.

I sat next to a woman last week who needed an extender, and her tray wouldn't fold down flat, but she fit into the middle seat unobtrusively.

Have a good trip, OP!

You'll be just fine OP, go on your trip and enjoy yourself!

I'm about a size 22 (down from 26 - it's a process). While I don't have to buy 2 seats, I make sure my string bean tween daughter is in the middle seat so I can keep the shared armrest up for comfort. If it was a stranger there, I'd have to be squished in with the armrest down.

I also purchased a seat belt extender of my own a few years ago. I tuck it in the side of my carry-on, then unobtrusively put it on after I sit down.

My mom was a 26/28 and she needed a belt extender but never two seats.

Thanks,

I have been wanting to go on a trip and I was thinking about taking Amtrak, but it is basically the same price as going by plane! and then I got really worried about the whole "you're fat, buy two seats thing" lol thank you for calming me!

Nope, you're fine. I had the same anxiety, but you will be fine. I worried about belt extensions*, overlapping, etc, but it didn't even apply. Be confident! It's your seat just like everyone else's.

*I do not think you will have a problem, but if you do, talk to the flight attendant, and they will give you an extension belt. This happened to my mother once (who was about a size 14) but the seatbelts in her exit row were much smaller than the ones in the other rows. They gave her an extension belt.

No. I'm also a 20. You're fine

I'l be honest, I'm a really anxious person and I'm also overweight. So I'm super nervous that I'll be forced to get two seats. I'm like a dress size 20. Have you ever had to get two seats?