However, a good rule of thumb is to choose a backpack that can comfortably accommodate their textbooks, notebooks, laptop or tablet, and other essential items. A backpack with a capacity of 20-30 liters is usually a good choice for most high school students.

A standard school backpack's size is typically determined by its capacity in liters, which varies depending on the student's age and grade level. For Primary School (K-5), a standard size is between 12 and 20 liters, designed to fit a lunchbox, a water bottle, and a few folders. For Middle School and High School, the standard capacity jumps to 25 to 35 liters to accommodate heavy textbooks, 1-inch binders, gym clothes, and a dedicated laptop sleeve (usually for a 15-inch device). In 2026, ergonomic experts recommend that a fully loaded backpack should not exceed 10% to 15% of the student's body weight to prevent long-term back strain. Popular brands like JanSport, North Face, and Fjällräven offer "standard" models that typically measure about 18 inches in height and 12 inches in width. When choosing a size, it is essential to ensure the bottom of the bag does not sit more than 4 inches below the waistline, as a backpack that is too large for the wearer's frame can lead to poor posture and chronic discomfort.