Height

• Lay your suitcase down flat on the floor, as you would to unzip and pack it. When the bag is closed, its height is measured from the floor to the top of all of the outside pockets. Many carry-ons have an extra zipper that can give you another inch or two of height, but depending on how full you fill the front compartments, you can also add to the height without the additional inches of cloth. Most airlines require the height of your carry-on not to exceed 9 inches or 10 inches.
  
  

Length

• A bag's length describes its size when it is standing up. If the suitcase has wheels, start your measurement from the bottom of the wheel and extend it to the handle on top. If the handle expands and contracts, move it to the contracting position, but be sure to account for any inches it sticks out above the frame of the suitcase. Airlines require carry-ons not to exceed 22 inches in length, for the most part, but some airlines allow your carry-on to be 24 inches long.
  
  

Width

• Your suitcase's width stretches from left to right, if the suitcase is standing up. Often, you'll find little buckles inside the suitcase that, when stretched width-wise, will secure your clothing inside. This dimension is usually the most straightforward, as luggage generally does not have pockets on the sides. Thus, the hard frame of the suitcase usually represents its actual width. Most airlines set the width limit between 14 inches and 16 inches, but a few have more stringent restrictions.
  
  

Weight

• Depending on its materials, your suitcase will be able to hold no more than a certain amount of weight before its wheels, handle or hardware break under the strain. For the purpose of using the suitcase as a carry-on, you will have to refer to each airline's weight restriction. Most U.S. airlines allow carry-on baggage to weigh up to 40 lbs., but for many European carriers, the weight limit is restricted to 25 lbs. or 30 lbs..