Get the 2.5-liter box for a hungry teen.

A hungry teenager needs around 2.5 liters; an average adult is fine with 1.5 to 2 liters.

The difference isn’t just appetite, it’s snacking. Teens tend to pack more separate things: a main, a side, fruit, a yogurt, maybe a granola bar. That adds up in volume even before you account for larger portions. A 2.5-liter box gives you room for a full meal plus a snack or two without having to play Tetris.

Most adults eat a single decent-sized meal at lunch. A 1.5-liter box fits a sandwich, a piece of fruit, and a small snack comfortably. If you’re someone who packs leftovers or a salad, go up to 2 liters. You rarely need more than that unless you’re an athlete or just really like volume eating.

One thing to keep in mind: capacity in liters is about total volume, not how well the box is laid out. A wide, shallow 2-liter box can be easier to pack than a deep 2.5-liter box. So check the compartments and dimensions, not just the number.

Buy the bigger one for a teen. The extra space gets used.