When choosing a backpack, it is important to select one that is the right size. Backpacks are measured in liters, and the size will be listed right on the product tag or label. For example, a 50 liter backpack is perfect for carrying around school books and supplies, while a larger 100 liter backpack is better suited for extended camping trips or travel.   To find out the liter capacity of your desired backpack, first convert all dimensions into centimeters (1 inch = 2.54 centimeters). Once you have the dimensions in centimeters, multiply the length by the width by the height. This will give you the volume of the backpack in cubic centimeters. Finally, divide that number by 1,000 to get the liter capacity.   Once you know the liter capacity of the pack, you can start to narrow down your choices by considering how much gear you’ll need to carry. For example, if you’re planning a multi-day backpacking trip, you’ll need a larger pack than someone who is just doing an overnight hike.