I called United Airlines about duffle bag sizes, because most are round on the ends, and only have two dimensions (length and diameter) rather than three (length, width, and depth). After a long discussion with a nice customer service lady involving several breaks for consultations with her "support person," I was told that I don't have to worry about size limitations on duffle bags, because they can be squeezed into available spaces when loading the plane. (The 50 pound weight limit always applies.) During the conversation, I was describing the 42" x 24" (length x diameter) military style duffle that I wanted to check, so I assumed she was telling me this bag was OK. Now, I'm worried that someone at check-in will see that big duffle and charge me $80 for an oversized bag, anyway. Do you think I'll have trouble?

Try to send an e-mail to the airline. I've done it once, and got a written response.

From United's Website:

Checked bags
For travel on United within the U.S. 50 states and to/from San Juan, Puerto Rico and St. Thomas U.S.V.I., you may check two bags free of charge.

The maximum size of each checked bag is 62 inches/157 cm (length + width + height).
The maximum weight per checked bag is 50 pounds/23 kg each.
Each checked bag must have the name of the person traveling on the outside of the bag, and we recommend on the inside as well.
United's 1K Premier Executive, Premier Executive and Star Alliance Gold members are allowed a third piece of checked baggage free of charge.
International allowance, size and weight rules vary by destination. Contact United or your travel agent prior to your trip for details regarding acceptance and restrictions .

You may substitute bowling, fishing, golfing, shooting, or skiing equipment for one piece of the two allowable checked pieces. Military personnel may substitute one duffel/B-4 bag free in lieu of their largest checked piece. Contact United or your travel agent prior to your trip for details regarding acceptance and restrictions for these or other checked items.

Oversize Baggage

Any checked bag with a single dimension more than 62 inches/157 cm is oversized.
Checked baggage which exceeds 62 inches/157 cm will be charged $80.00 per piece.
Any bag which is more than 115 inches/292 cm will not be accepted.

I am assuming that you are not military. Your size would be 66", only 4" over. Are you going to stuff the bag? If it's not stuffed, it won't really plump out to look the 66". I highly doubt the ticket counter personnel would actually measure the bag -- I travel twice a week and have never observed this. They seemed to be more focused on the weight.
If it were me and this was the bag I really wanted to take. I would take it; not over-stuff it; just act cool when checking it in(i.e. don't make comments on the size). If given a hassle, then be prepared for the $80.

I have no idea how the check-in agent will treat i357, but 42" is 3.5 feet. It's HUGE BAG, regardless. If you have to put that bag in a box, the box will have to measure 42x24x24, i.e. 90" overall, and way oversize.

Do not assume that they'll take it without problem.

Probably impossible, but I'd try to get an email or written statement that the duffle will be no problem.

Is this your only bag? If so, consider packing a smaller duffle, or "stuff bag" into it, so that you can split the contents into two bags, if necessary, then combine them after you reach your destination.

Since it is not a hard, rectangular object, like a box, it does fit into a lot of spaces that the box or suitcase wouldn't, and its overall volume is not the same as if it were in a box. "rkkwan"'s box would require 24,192 cubic inches, your bag only uses 18,991.

If you want to play the volume game, the largest rectangular/square box within the 62" rule is 20-2/3 in on each side, which has a total volume of about 8,827 cubic inches. 18,991 is more than double that volume.

I agree with rkkwan's last calculation on meeting the "62 inch rule" -- I was just disagreeing with the concept of putting "a cyclinder into a box".

Trying my best to make favorable analogies of "box" measurements to cyclinders, the best comparison to the L+W+H rule of 62" I can make is still about 80" (42" + (12"*pi))-- so it's oversize by those rules no matter what. Your baggage counter clerk isn't about to discuss geometry anyway; 80 or 90 are both over 62. (Thank you rkkwan for catching me on that.)

I guess all of us agree that you cannot assume you be problem-free with it - so be prepared, and good luck.

How about securing corrugated container of max permitted size. Load with duffle contents and duffle. Check weight with bathroom scale. I have seen passengers wearing many garments..then shedding them once seated! Try loading the 'duty free' container or bag with heavy items.

rb_travelerATyahoo's suggestion of putting a "stuff bag" inside the duffle bag is a good idea. When I travel, I always carry a "bag within a bag." It is usually a large collapsible tote bag or smaller duffle. On the way to my destination, it's empty. On the way home, it's usually filled with purchases and souvenirs and goes on the plane with me as a carry-on. (I know your question was about dimensions, but this could help if you were worried about your larger bag being over the weight limit on your return home. Having worked at the post office for many years, your 42x24" duffle made me think of our mail sacks,which are very similar in dimension, and I can see how easy it would be for the weight to exceed 50 lbs.)

Donna

We always take a military duffle bag with us on vacation. I use it as a laundry bag over the bathroom door and then close it up and check it as luggage. I have never yet had to pay extra for it. It is soft and it squishes down pretty far.