The Louis Vuitton Keepall is one of the most classic and distinctive models. The model is also often called the "Boston Bag" which is reminiscent of a travel / duffel bag.
The sizes are the width in cm, so Keepall 45 is 45cm in width. Many airlines approve carry-on bags up to 55cm, and here you will be able to take up to Keepall 55 with you.
Although hand luggage is often only up to 40cm, it will often also be possible to take the Keepall 45 with you.