If you need a bit more space than what a small backpack offers but don't want to lug around a large pack, go for a medium size. These have a capacity of 25 to 40 liters, which is just enough room for a change of clothes, a laptop, and these must-have travel accessories for every destination.
In general, a backpack is considered a personal item if it fits under the seat in front of you. This means that the backpack must be no larger than 22 inches in length, 14 inches in width, and 9 inches in height. If the backpack is larger than this, it will be considered luggage and must be checked.
As a general rule of thumb, anything smaller than the dimensions of a carry-on can be considered a personal item. However, every airline has different restrictions for size. In most cases, your backpack should be no more than 18 x 14 x 8 inches.
Size and Weight RestrictionsTypically, the bag must be within the cabin baggage dimensions of around 22 x 14 x 9 inches (56 x 36 x 22 cm), commonly considered the standard size for carry-on.
Most bags range from about 30L (1,800 cubic inches) all the way to 100L+ (6,000+ cubic inches). I recommend a backpack around 40L-50L. Personally, I wouldn't go over 65L, but some people like a bigger bag.
A school backpack of 21 to 30 liters is suitable for you. This is the most common size for backpacks. The bag has enough space, but does not exceed the required size. Most school backpacks have several small pockets.
A backpack with a capacity of 25 to 30 litres is usually enough to carry the essentials for a normal school day. If you plan to carry extra stuff like sports equipment or a lunch box, it might be wise to choose a backpack with a larger capacity. Make sure your bag fits and is not too big or small for your body type.