A 1-liter lunch box fits the average adult lunch

For a typical adult work lunch, aim for a 1-liter (about 4 cups) lunch box. Kids do fine with half that — 500 to 700 ml (roughly 2 to 3 cups).

A liter sounds bigger than it is. Once you put a decent sandwich, a yogurt, some fruit, and a snack inside, you’ll probably be near the top. That’s the sweet spot for most office lunches. If you’re a bigger eater or like to pack leftovers in separate containers, step up to 1.5 liters. But anything larger and you’re carrying air.

For kids, portion sizes drop fast. A 500 ml box handles a small sandwich, fruit, and a treat. If your kid is a teenager who eats like a grown adult, stick with the same 1-liter recommendation. For younger kids, the smaller box also fits their backpack better and keeps them from getting overwhelmed by a mountain of food.

One more thing: getting a bigger box than you need is a mistake. It just invites you to fill it, and then you’re either overeating or throwing food away. Match the box to the meal, not the other way around.