Consumer need for cabin-size or carry-on luggage is increasing as people look for convenience when travelling and to avoid charges for checked baggage. Take a look at it luggage's Roll-it category for cases specially designed for cabin requirements around the world.

International Cabin Size
Upto 56 x 45 x 25cm, as used by British Airways, Easyjet and many international airlines.
Maximum All Airlines
Upto 55 x 40 x 20cm, the maximum size guaranteed on board most airlines, including Ryanair.
Underseat size
Stow your bag under the seat in front of you, to avoid the crush or lack-of space in overhead bins.