According to the number
When you are outing alone, you can choose a backpack of 25 to 35 liters. When traveling with family and children on holiday, from the perspective of caring for the family, you need to choose a backpack of about 40 liters. There are more plug-in systems to help your family bring umbrellas, cameras, food and other items.
Because of the different body and weight of men and women, the choice of outdoor backpacks is not the same. Usually a short excursion for a day or two, a backpack of 30 liters for men and women can be used. For long-distance travel or camping over 2 to 3 days, when choosing a backpack of 45 to 70 liters or more, generally men choose a backpack of 55 liters and women choose a backpack of 45 liters.
One-day round-trip excursions, cycling, and mountaineering activities, choose a backpack of 30 liters or less. Two to three days of camping can choose 30-40 liters of multi-purpose backpacks, hiking for more than four days, to place tents, sleeping bags, moisture-proof mats and other outdoor equipment, you can choose more than 45 liters of backpacks. In addition, the general field activities are different from the backpacks used to climb the mountains. The backpacks used in mountain climbing do not have many parts. Friends who like mountain climbing need to pay attention.
According to the length
Before choosing a backpack, you first need to measure your upper back length, which is the distance from the cervical vertebrae to the last lumbar vertebrae. If the trunk length is less than 45 cm, you should buy a small bag. If the trunk length is between 45 and 52 cm, you should choose a medium bag. If your torso is more than 52 cm in length, you should pick a large bag.