It depends on the airplane and to some extent the airline. Go to your airline's web site and find out the equipment that is planned for your flight. Then look for the "seat map" that matches the airplane type. You should be able to find the width of the seat and the "pitch" /distance between the end of the seat and the next row of seats.
I am by no means an expert, but the your car seat must be FAA approved. There should be sticker on it somewhere that tells you that it is. If it isn't, they won't let you use it. Plus I am pretty sure that the FAA approved ones will fit in the seat. I think the car seat must be in the window seat and I know it cannot be in an exit row.
It does have to be FAA aproved and put in a window seat.
I know that the backless " booster seats" are not allowed to be used during takeoff and landing, at least on SWA, from overhearing the FA explain that to a passenger. The lady had to remove it and place it under the seat in front of her and seatbelt the child in his plane seat. It probably wasn't FAA approved but I am not sure.
I don't think any of the boosters are allowed on any of the airlines. I don't have one since I'm expecting my first baby, but all of the stuff I've read about child safety seats says that the boosters have to have a seatbelt with a shoulder strap, which explains why you can't use them on planes.
Save Up to 30% on Rooms at Walt Disney World!
Save up to 30% on rooms at select Disney Resorts Collection hotels when you stay 5 consecutive nights or longer in late summer and early fall. Plus, enjoy other savings for shorter stays.This offer is valid for stays most nights from August 1 to October 11, 2025.
CLICK HERE