When it comes to carry-on bags, some airlines are now going back to the future.

Get ready for a return to the home of the brave and the land of the fee.

American Airlines is putting bag sizers back at the gates and if your carry-on doesn’t fit in it, you’re going to have to pay a checked bag fee.

Other airlines are also starting to crack down as more people return to the skies. Remember, there is no one standard domestic carry-on luggage size. American’s is 22 x 14 x 9 inches. But the carry-on size limit for Southwest is 24 x 16 x 10 and you get two checked bags free. Every airline is different.

Are you traveling internationally? Make sure your bag or suitcase stands at 21 inches or less.