According to the different backpack volume, the knapsack can be divided into big, medium and small.
Large backpack capacity is more than 50 liters, suitable for long distance travel and more professional adventure. For example, when you want to go to a region like Tibet for a long time
When traveling or mountaineering, you should choose a large backpack with a capacity of more than 50 liters. Some medium and short trips require large backpacks if you need to camp in the wild, because only it can hold the tent, sleeping bags and sleeping pads you need for camping. Large backpacks can be divided into mountaineering bags and long haul backpacks, depending on their uses.
The size of the mid sized backpack is generally between 30~50 liters, the use of these backpacks is more extensive, 2~4 days of field travel, urban travel, and some remote non camping travel, medium backpacks are more suitable. Clothes and some daily necessities can be packed. The pattern and variety of the medium-sized knapsack are more diverse. Some backpacks have added some side pockets, which is more conducive to the separation of items. The backpack structure of these knapsack is roughly the same as that of a large backpack.
The small backpack is less than 30 litres, and most of these knapsack are used in the city. Of course, it is very suitable for 1~2 days outing.