Need to Know: School Backpack Capacity Guidelines for Kids of All Ages. For preschoolers, it is recommended to look for backpacks with a maximum size of 15L. For elementary schoolers, larger sized bags (maximum 20L) become more suitable. For middle schoolers, a couple of options between 25-35L is ideal.

A "normal" or standard size for a school backpack typically ranges from 20 to 30 liters. For elementary school students, a smaller 15 to 20-liter pack is usually sufficient for a lunchbox and a few folders. Middle and high school students, who often carry multiple heavy textbooks, a 15-inch laptop, and gym clothes, generally prefer a 25 to 35-liter pack (like the iconic JanSport Right Pack or North Face Borealis). In 2026, many students favor "expandable" designs that can stay slim for light days but grow for project days. A peer-to-peer "safety essential" is to ensure the backpack doesn't exceed 10–15% of the student's body weight and has padded straps to prevent shoulder strain. If you're buying for university, a 28-liter bag is often considered the "sweet spot" for balancing tech protection with enough room for a day's worth of supplies.