Lunch Box Sizes: Kids, Bento and Adult Lunch Bags
There is no standard lunch box, so the useful questions are how much food a child or adult needs and what has to fit inside. These figures cover typical outside and inside sizes, bento capacity by age, and the containers that fit.
A typical kids' insulated lunch bag measures about 9 × 7.5 × 4 in (23 × 19 × 10 cm) and holds 4 to 5 liters. A kids' bento box is about 8.5 × 6.5 × 2 in (22 × 17 × 5 cm) with 500 to 650 mL of food space. Adult lunch bags run about 10-12 × 8-9 × 5-7 in, or 6 to 12 liters.
- Kids' lunch bag
- 9 × 7.5 × 4 in
- Kids' bento
- 500-650 mL
- Adult lunch bag
- 6-12 L
- Cold sources
- At least 2
On this page
Lunch box size chart
Outside dimensions decide whether a lunch box fits in a backpack; inside volume decides how much food goes in. Soft bags lose about half an inch each way to insulation. Sizes below are typical across current models, not a standard, so check the listing of the one you buy.
| Type | Outside (in) | Outside (cm) | Volume | Suits |
|---|---|---|---|---|
| Snack box / small bento | 6-7 × 4-5 × 2 | 15-18 × 10-13 × 5 | 300-450 mL food | Preschool, snacks |
| Kids' bento box | 8.5 × 6.5 × 2 | 22 × 17 × 5 | 500-650 mL food | Ages 5-10 |
| Kids' insulated bag | 9 × 7.5 × 4 | 23 × 19 × 10 | 4-5 L | Ages 4-12, one bento plus a drink |
| Tall kids' bag | 10 × 8 × 4.5 | 25 × 20 × 11 | 5-6 L | Upright bottle or food jar |
| Adult lunch bag | 11 × 8 × 6 | 28 × 20 × 15 | 8-9 L | Two containers and a drink |
| Large lunch cooler / tote | 12 × 9 × 7 | 30 × 23 × 18 | 12 L | Shift workers, long days, sharing |
To work out the volume of any box, multiply the inside length, width and height. In centimeters, divide by 1,000 for liters (23 × 19 × 10 cm = 4.4 L). In inches, divide by 61 (9 × 7.5 × 4 in = 270 cu in = 4.4 L).
How much food space a child needs
School lunch standards give a good target. The USDA National School Lunch Program sets calorie ranges for a lunch, and a widely used bento rule converts calories to box size: a tightly packed bento holds about 1 calorie per milliliter when it is about half grains, a quarter protein and a quarter fruit and vegetables.
| Age / grade | School lunch target | Bento capacity | Container equivalent |
|---|---|---|---|
| Preschool (3-4) | About 350-450 kcal | 350-450 mL | 1.5-2 cups |
| Grades K-5 | 550-650 kcal | 550-650 mL | 2.3-2.75 cups |
| Grades 6-8 | 600-700 kcal | 600-700 mL | 2.5-3 cups |
| Grades 9-12 | 750-850 kcal | 750-850 mL | 3.2-3.6 cups |
| Adults | Varies, often 600-900 kcal | 600-900 mL | 2.5-4 cups |
The K-5 to 9-12 ranges are the USDA meal-pattern figures; the preschool range is an approximation for a child that age. The bento rule is a packing guide, not a nutrition rule: loose salads take more space per calorie and dense foods such as sandwiches less. A Bentgo Kids box, for example, has 2.4 cups (568 mL) split into five compartments of 1 cup, ½ cup, ½ cup, ¼ cup and a 2-tablespoon dip well, which fits the K-5 range well.
Snacks and a drink go on top of the lunch figure. Allow room for an 8 to 12 oz (240 to 350 mL) water bottle beside the box, or a separate side pocket.
Bento boxes vs lunch bags
Bento box (hard, compartments)
- Fixed portions, easy for young children to open
- Flat shape slides into a backpack's laptop sleeve
- Few separate containers to lose
Lunch bag (soft, insulated)
- Takes any combination of containers, jars and bottles
- Insulation and room for ice packs, which a bare bento lacks
- Grows with the child: the same bag works from age 5 to 12
Many families use both: a bento inside a slim insulated sleeve or bag. If you do, the bag's inside dimensions must exceed the box by about half an inch each way plus the thickness of an ice pack, so a kids' bento of 8.5 × 6.5 × 2 in needs a bag about 9 × 7 × 3.5 in inside.
What fits inside: containers, jars and ice packs
- Food containers: a 2-cup rectangle (about 5 × 4 × 2 in) and a 1-cup round fit side by side in a standard kids' bag. Two 3-cup meal prep containers stack in an adult bag at least 7 × 5 × 5 in inside. The food container size guide lists outside dimensions by capacity.
- Food jars: a 10 oz (300 mL) insulated jar for kids is roughly 3.5 in wide and 4.5 to 5 in tall; 16 oz adult jars are roughly 4 in wide and 6 in tall. They only fit upright in taller bags.
- Ice packs: slim lunch-size packs are about 4 × 6 × 0.5 in. Put one under and one over the food.
- Drinks: a 12 oz (355 mL) can is 4.83 in (12.3 cm) tall and 2.6 in (6.6 cm) wide; a 16.9 oz (500 mL) water bottle is about 8 in (20 cm) tall, too tall to stand in most kids' bags.
Fitting the lunch box in a backpack
- Measure the backpack's main compartment, not the outside. A kids' backpack of 15 to 16 in has a compartment roughly 11 × 14 in and 4 to 5 in deep.
- Subtract the books and folders. A letter-size folder takes 9.5 × 12 in of flat space. What remains, usually 3 to 4 in of depth, is what the lunch box can use.
- Choose a flat box for full backpacks. A 2-inch-deep bento rides beside folders. A 4-inch bag often has to clip outside or be carried separately.
The backpack size chart covers volume by age. For field trips and long days without a fridge, a small soft cooler of 6 to 12 cans holds a full lunch and keeps it cold far longer.
Keeping packed lunches safe
Insulation slows warming but does not keep food cold on its own. The USDA Food Safety and Inspection Service guidance for bag lunches is specific:
- Perishable food should not sit at room temperature for more than 2 hours, or 1 hour above 90°F (32°C).
- Pack at least two cold sources with perishable food, such as two frozen gel packs or one gel pack and a frozen water bottle or juice box.
- Use an insulated, soft-sided bag; paper bags do not hold the cold.
- Keep hot foods hot with an insulated jar: fill it with boiling water for a few minutes, empty it, then add the food piping hot.
Two slim ice packs add about 1 in of thickness. A bag whose inside depth equals the food container depth leaves no room for them, so choose one at least 1 inch deeper inside than your tallest container.
Frequently asked questions
What are kids' lunch box dimensions in cm?
Most soft insulated kids' lunch bags are about 23 × 19 × 10 cm (9 × 7.5 × 4 in), holding 4 to 5 liters. Hard kids' bento boxes are about 22 × 17 × 5 cm (8.5 × 6.5 × 2 in).
How many liters is an average lunch box?
A child's lunch bag holds about 4 to 5 L in total. The food containers inside usually add up to 0.5 to 1 L. Adult lunch bags hold 6 to 12 L, and the larger ones fit two meal prep containers plus a drink.
What size bento box does a child need?
A common rule from Japanese bento practice is that 1 mL of a tightly packed box holds about 1 calorie. A 5- to 10-year-old's lunch of 550 to 650 kcal fits a box of about 550 to 650 mL; preschoolers need around 350 to 450 mL.
What size thermos food jar fits a kid's lunch box?
A 10 oz (300 mL) food jar is the usual size for children. It is roughly 3.5 in wide and 4.5 to 5 in tall, so it stands upright only in a bag at least 5 in deep inside; in a standard 4-inch-deep kids' bag it has to lie on its side. Adults usually use 16 to 24 oz (470 to 710 mL).