This test method determines and standardizes an unextended and extended capacity for backpacks and related bags. Related bags include lumbar packs, soft rucksacks, internal and external frame packs, duffel bags, and travel packs. This test method is designed to provide a means whereby manufacturers and consumers may have a consistent means to compare pack volumes. This test method does not take into consideration areas of the backpack that are not completely enclosed by fabric such as mesh pockets, water bottle holders, and compressor pockets. For practical purposes this test method cannot be used to measure capacities less than 4 L. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.